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Well the only way to erase his BIOS password is to open it up, but unless you are confident in what you are doing and at the very minimum have a Anti-static wrist strap/mat I wouldnt go anywhere near...

If its not the XP logon promt he must have a BIOS password, hence the prompt you get before XP starts.
Although finding out his XP password is simple enough, I dont know of any way to find out his...