If you have a Windows Setup CD, just put it in, and Boot from it. You can then ask the setup to format the drive and re-install Windows clean.
Of course you'll need to backup your files if you want to keep them, as a format will delete everything there is on the drive.
----------------------------------
Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.