I regularly have to re-install Windows for one reason or another. Luckily I have a Windows disk so re-installing is easy. You can use someone else's Windows disk and use your own product key, which should be on a sticker on the computer, or try a system recovery disk:
http://forums.techare...tutorials/1114725.htm
What you also need to do is back up all your personal files to a separate hard drive so you won't lose them. You can have two hard drives linked so that one is an automatic backup for the other, or you can manually back up. See here for more info:
http://en.wikipedia.org/wiki/RAID
Remember that when you do delete all your files from your system drive that your backup is now your only copy of them. What you don't want now is for your backup drive to fail and lose that too. When your system is back up and running copy your backups back over.
I got so fed up with losing all my updated drivers and dowloaded programs that I now SAVE any driver or program I download to a folder on my back up drive before installing it. That way when I format the system drive and re-install Windows I then just go through the downloads and re-install them.