irql not less or equal + xp

Clarifications

unfortunately it could be many things...

faulty memory
faulty power supply
faulty motherboard
bad driver

if only troubleshooting BSODs were easy

Has any hardware been changed?

by adding more information about the error.

But a few things to try
Run chkdsk
update drivers
run a motherboard test
run a memory test
run a hard drive test
let us know the results of these tests and the full error

http://www.memtest86.com/

This is a good place to start. Make a boot disk out of the iso and let it run for a good while.

While installing windows XP (first edition no spk) on a new build ( core 2 quad 6600 on a Intel DG43NB 2x2gig corsair pc2-6400 ddr2 cl 4-4-4-12) I received the error when windows installer was installing the drivers. I was told by many that it sounds like a memory issue. but playing with the ram timeings and voltage did not help. So I disabled multi-processor support as the bios was old (0054- new is 0064)installed windows xp with SPK2 on the PC, updated bios with bootable cd, enabled multi processor support. and I'm back in the saddle.