Has he partitioned the disk into two disk "drives" and installed a copy on each?
--OR--
For NTFS drives:
1) Start your computer to Safe Mode with Command Prompt
2) Type “cd\” press “Enter”.
3) Now type cd\windows\system32 , press “Enter”
4) Type “osuninst.exe”, press ENTER.
5) Now follow onscreen prompts to uninstall XP
For FAT32 drives:
1) Start your computer with a boot disk, and load to command prompt.
2) Type “C:” press “Enter”.
3) Now type “cd windows” press “enter”,
4) then “cd system32” and press “Enter” .
5) You should now be at C:\windows\system32. If so continue
6) Type “osuninst.exe”, press ENTER.
7) Now follow onscreen prompts to uninstall XP