WinXP administrator password recovery

The Offline NT Password & Registry Editor, Bootdisk / CD will do what you want.

Google for chntpw. I use it from a bootable Rescue Is Possible Linux CD. You can google for the RIP cd, burn it, boot from it in console (text) mode, mount the hard disk (usually like "mount /dev/hda1" or "mount /dev/sda1", check what listings are in /mnt for some clue), then use something like "chntpw /mnt/hda1/WINDOWS/system32/config/SAM" and accept the options to clear the password for that account. Then remove the CD and reboot once changes are written to the drive. When it restarts, local administrator has no password.

I think the chntpw site has a bootable disc also that specialized just in resetting the password, and RIP is a multipurpose tool so has a bigger learning curve.