I would suggest the same. Reinstall XP using a new key, then upgrade to SP1.

BTW, I dont recommend using reset5. It hides activiation and tricks XP into thinking its still day 1 of the 30 day period upon every reboot. If you run the %systemroot%\system32\oobe\msoobe.exe /a command, it will not work, meaning its been disabled. Reset5 may seem to work, but you may also be subject to periodic crashes.

Cheers.