I recently tried changing a hard drive running Windows XP from a 500Mhz Celeron to a P4 2.26. Both computers have 512MB RAM.
When I fire up the P4 with the transplanted hard drive, it goes through POST and gets as far as the Windows splash screen, then I get a BSOD that flashes faster than can be read and the PC reboots and repeats the cycle.
One other clue: for an unknown reason the PC will boot up if the original XP disk is in the CD drawer.
Any suggestions?