You need to install xp cd,reboot computer,boot from cd,recovery,press the
enter key for password,at the curser type:FORMAT C: /FS:ntfs
When thru,type:EXIT
Reboot to cd,install xp,if you only have the upgrade version of xp,recovery,
type

iskPart Then delete the xp partition that's unwanted,if still not right, do
DiskPart,then type:EXIT Then type:EXIT Reboot to cd,then select install xp,new
copy,xp will format the drive.
This gives some options,xp cant do anything to C: drive while explorer runs,booting
to the cd it can.You can always type:HELP DiskPart /? or FORMAT /?