Use boot n nuke to write 0's to the whole drive
Now there should be nothing on the harddrive
Next: Put in your XP CD and ensure the bios is set to boot from CD first
reboot the computer
At the prompt type any key to continue booting from CD
Follow the prompts
When you get to the part of formatting, you will see the option to Format Full NTFS
It should be selected by default, if not select it
Let it do it's thing, after formatting it should automatically start copying files from CD to disk