What exactly is formatting and why is it necessary?
Formatting is the method of whipping your hard drive clean of previously
  installed / stored data. Do not think that the data is completely  
removed when formatting, because in fact its not. But, we do not need to
  cover this. When you format, you do lose everything that was 
previously  installed, so if you have important documents, back them 
up!.
There are various reasons that formatting is necessary.  Some may be  
because your computer is lagging horribly and sound and such just start 
 failing, you have to run all sorts of tools to tweak it and ran  
diagnostics, but itâۉ„¢s just not cutting it. You want it back to  
stock performance and everything to work correctly, so you just say  
screw it and reformat it. Various viruses and worms can wreak havoc and 
 are not able to be rid of unless you format your pc. Sometimes  
itâۉ„¢s necessary to completely delete the partition and re-create  
it, then format. As stated previously, there are methods that the more  
advanced users may do to dig up past data, usually just file names, but 
 that is more then enough to tell what was previously on your hard drive
  disk.
What is required for formatting?
I will show you some of the tools that you should have when  
reformatting. This may vary, depending on what file system you have and 
 what operating systems been previously installed.
- Win9X Boot Disk
This is used to boot up your PC into DOS for various formatting  
operations. The situations call for different measures. Sometimes a boot
  disk is a must.
- Restore CD
A restore cd comes with your new computers. They have the factory  
settings, drivers, OS and everything you need for your PC to be put to  
its factory settings. Some users may have lost this or never got one, so
  I will cover some optional solutions.
- Windows Operating System ( OS )
You may have bought or even burnt a copy of a windows operating system. 
 This does not mean that your computer will install 100% complete 
without  any problems, this is simply the basic foundation for a newly 
installed  OS. You may be required to supply drivers and such. Read 
later on about  this.
What if I do not have a restore or windows operating system cd?
If you are lacking everything that you need, please do not try to  
reformat. With that being said, let me tell you what should be done if  
you are supplied with efficient tools necessary for a reinstall. If you 
 do not have a restore cd, but you have a copy of the Windows OS, then  
there are various steps you should take for a successful install. First,
  determine your PC brand, which could be Hewlett Packard, Gateway,  
E-Machine etc. Once you have figured this out, simply determine the  
model. I know that Compaq and HP have an auto-detection system to  
determine the settings for you, if you have this type of machine, others
  might too just make sure to check there official web site and look for
  Downloads or Support. With a manufactured pc you should be able to 
give  them a call and request a new restore cd, depending on how old the
  computer is.
If you can not figure out your model and make try using the msinfo32  
(start—> run—> msinfo32) or a utility called Sisoft Sandra Pro to 
 detect your model and make for you. This is also handy if you have a  
custom built pc which has no restore cds created for it. Use Sisoft to  
determine all of your hardware settings and the type that’s installed,  
and then use it on 
http://www.google.com
  to search for the drivers you need. You must search for drivers that  
are designed for the exact operating system you are installing or they  
will be incompatible! Mainly, with an older computer, if you are  
installing Windows 95/98/ME then you SHOULD download all drivers ahead  
of time. If you have Windows XP and are installing it on an older system
  then the Plug and Play should pickup most of the settings for you, so 
 needing drivers downloaded ahead of time would not be needed. If the  
drivers are something like video driver then you should download updated
  ones from the default manufacturer because MS only supplies you with  
the lowest quality drivers possible.
I have everything I need, what next?
Now, you must determine the operating system that is currently  
installed. If it is Windows XP then there are more steps that must be  
taken in order to format successfully from DOS. If you are on Windows  
95/98/ME then the steps are a lot less struggling. If you wish to remove
  the partition completely and reformat it and previously had Win9X then
  do so, just follow the steps that are required for reformatting an XP 
 system from DOS.
FIRST STEP FOR BOTH XP & 9X:
Determine if your copy of the restore/windows cd is bootable, or your  
computer is setup to boot from CD at startup. Simply place the CD in the
  CD-Rom, reboot your computer and see if it tries to read the cd before
  starting windows. If, instead it reads something like the A: drive  
first, then you must change the boot-up sequence to CD-Rom first. This  
method varies by the type of motherboard you have. To enter your BIOS to
  change the settings use either F1 or Del. These are the two mostly 
used  ways of entering, if that’s not doing it, it should say what key 
to  press to enter bios setup. Look for the option Boot, they should be 
 presented like Floppy Disk; Removable Devices, CD-Rom, Hard Drive etc. 
 If its an older motherboard, they are identified totally different, you
  will have to look up the sequences online. Once you have changed these
  and place CD-Rom at the top by usually using the + and - keys on the  
number pad to your right, save the settings and reboot. If it does not  
pickup the CD-Rom and ask you for various operations, then the CD is not
  bootable, which is where a boot disk comes in. If the CD is not  
bootable, make sure to set the boot first priority to Removable Devices 
 or Floppy Disk.
Any asterisk that is provided means the steps are used in conjunction with each other.
Restore CD’s
1) Place the Restore CD into the CD-Rom once you have determined that its bootable
2) You will be given a list of various options for restoring. Make sure 
 you choose something like Clean Restore, they should provide  
descriptions of each.
3) Just follow the required steps for installation, its all self-explanatory with a restore CD.
4) If the Restore CD does not provide any means of a clean install, just
  a over ride of the current windows install, follow the below methods 
up  to format it.
Booting From a Floppy **
1) Grab yourself a bootable floppy disk at 
http://www.bootdisk.com designed for Win9X. Any will work just as long as it provides access to DOS and CD-Rom activity.
2) Provide a 1.44MB floppy disk that is not needed and install the boot disk files to it.
3) Place the floppy disk in the floppy drive and restart.
4) Once its reading the floppy a menu will come up and ask if you wish  
to boot with CD-Rom support, choose the option to boot into this mode.
Windows 9X Non-Bootable CD(**)
1) You will be given a command line interface, depending on what your  
default drive letter is, it would look something like C:>, if its  
A:> simply type in C: and hit enter.
2) Simply issue the command format C: where C: would be the default  
letter of the drive. It will ask you for confirmation, just type Y.
3) The formatting phase will start, it could take a while depending on the size of the hard drive.
4) Once finished, it will prompt you for a volume name, which simply is 
 what the hard drives label will be, its not necessary but you may enter
  something if you wish.
5) Now, you will be dropped back into a C:> prompt. Enter in the Win9X CD to the CD-Rom.
6) You must now drop into the CD-Rom drive to issue commands from it. To
  do this simply type in D: or whatever drive letter has been assigned 
to  the CD-Rom
7) Once it shows up as D:> type in Setup and the setup phase will  
initialize, just follow the simple steps and you will make it. 
Windows 9X Bootable CD
If the CD is bootable, then you will be given similar options that a  
floppy boot disk would provide. Make sure to startup into DOS with  
CD-Rom support. Do not startup from hard drive or this will just load  
your current OS. Just use the above methods once you have chose to  
startup into DOS. Then follow the required steps provided when you are  
in the command prompt.
NOTE: Be sure that you have the correct drivers for your machines  
specifications or you will come across a lot of driver problems.
Windows 2K/XP Non-Bootable CD w/ Win9X Boot Disk (**)
1) Once you have got the DOS prompt in front of you issue the fdisk command
2) You will be asked “Do you wish to enable large disk support?” type in
  Y. This simply allocated all the possible space for large sized hard  
drives.
3) We must determine the type of file system you have. Choose the option “Display partition information”
4) Look under the tab labeled “Type” if it is FAT32 then it will be a DOS partition, if its NTFS then its a Non-DOS partition.
5) Hit Esc to go back to the first options
- If it was NTFS choose the option “Delete Non- DOS Partition” which is option 3.
- If it was FAT32 choose “Delete Primary DOS Partition” which is option 1
5) Next you will be asked to enter the number of the partition, which is
  will probably be 1, unless you have two hdd installed. If you are not 
 sure which one is which, the default selected partition will be the one
  your windows is installed on, so choose that one.
6) It will ask you for the volume label, if there is even one entered, them type it in as it should be typed.
7) Now, it will ask you if you are sure you want to delete this partition, type Yes.
8) It will now tell you that the partition has been deleted, hit Esc to continue.
9) You have the list of options at your view again. Choose “Create DOS Partition or Logical Drive”.
10) Now choose “Create Primary Dos Partition”
11) It will now ask you if you wish to enable the full size of the HDD for that partition and make it active, choose Yes.
12) It will create the partition, it might take a little while, but not 
 long. Once this is done, it will ask you to restart your computer.
13) Restart with the boot disk inserted, get back into DOS Prompt and now type in format C:
14) Once its done formatting and you have optionally entered a volume name, enter the Win2k/XP CD into the CD-Rom.
15) Browse to the assigned CD-Rom drive letter by simply typing D: where D would be the drive letter
16) Now type in the following: “cd i386” and it should drop you into something like D:/I386
17) Now type in “winnt” and the setup phase should startup, just follow the required steps.
Windows 2K/XP Bootable CD
1) When you startup with the CD entered, it should say “Press any key to boot from cd” or similar.
2) It will load all the necessary files to give you a graphical users  
interface for the setup, instead of a DOS based environment.
3) It will ask you if you wish to install Windows XP to press Enter, so do so.
4) Now comes the license agreement, simply press F8 to move on.
5) You will see your partitions, choose the one you wish to install 2K/XP to then press Enter
NOTE: If you wish to delete the current partition and recreate it, then 
 simply press D, Enter, then L to the next given screens then choose 
this  as the partition you wish to format and install.
6) Now you will get a list of options to to format the file system. Choose “Format the partition using the NTFS file system”
7) Now it will format and copy the required files to startup the setup  
once you reboot. A warning will popup telling you its about to reboot.
8) Let it reboot and do not press any keys and wait for it to reboot,  
the Windows XP logo will show up and then initiate the rest of the setup
You should print this out so you may refer to it when needed.