i know it's a late answer, but i just ran into the same problem on the same MOBO and figured out what is causing it. i'm posting the answer so other folks like me who went googling for someone with a similar problem can find the answer.
when you did a complete overhaul, you changed the CPU from a non-hyperthreading CPU to one that uses hyperthreading. even though the bios will discover this, and allow you to enable hyperthreading AND XP will recognize this and show as 2 CPUs in the hardware manager, you will get random crashes. could be after 2 minutes of light usage, could be after 2 hours of gaming - completely random. worst part is if you try to reinstall XP with the notion that maybe the old files and registry entries for the uniprocessor HAL and now XP will not allow you to copy certain files necessary for the installation.
change back to your old CPU. XP will not crash and you can now load the latest BIOS that 'should' solve the crashing problem. if you are in limbo, you can now reinstall XP without those file copy errors, then try to update the BIOS and maybe the hyperthreading CPU will work.
