1. Delete the C:\Windows and C:\Program Files folders, along with any other folders on the C: drive that you do not need anymore.
2. Convert the C: drive to NTFS if desired, using the convert program.
3. Edit C:\boot.ini to remove the Win9X reference.
Some reports also say you can format the C: drive and boot from the Win XP CD, which will allow you to repair the boot files.