Right click my computer on the desktop
click on 'manage'
click on disk management
You should see a HD with however many gigs your hard drive is with no actual 'File system'
Right click on it
Click the 'delete partition' option
And then make a new one. If you need help making a new one, just holler
EDIT: And beware the bootloader. It could get mad at you for doing that. If it gives you an error, boot from the XP Cd and go to the recovery console and type:
fixmbr
Which will replace your master boot record and it 'should' delete the bootloaders entry in there.