You could try using your XP CD. Instead of going into XP setup press R for recovery. Select your installation and enter your password. You should be left at C:\Windows> Type format C: and press enter. (you say C is the drive you want to format). It should leave D alone and at the end you will be back at C:\Windows. Type exit and press enter. The computer should restart with XP untouched and a clean drive C. I would wait to see if anyone else confirms this procedure before trying it though.