I was faced with a very similar situation only a few days ago. To complicate matters the owner of the computer did not know the password to the 'Administrator' account. This is a problem because the 'Repair' mode, accessible from the WinXP install CD, requires the Administrator password.
I resolved the problem by booting from the GAG install CD (http://gag.sourceforge.net/) and using the 'Uninstall GAG (restores standard MBR)' prompt. It did the job very efficiently.
Executive summary: Use GAG.
I resolved the problem by booting from the GAG install CD (http://gag.sourceforge.net/) and using the 'Uninstall GAG (restores standard MBR)' prompt. It did the job very efficiently.
Executive summary: Use GAG.