IRQL Problem with MSI KT4 Ultra

Currently I have a problem with one of my machines

Spec:

MSI KT4 Ultra (without LAN or SATA)
AMD Athlon 800 (Soon to be Upgraded)
256Mb 266Mhz RAM (Soon to be Upgraded)
Sparkle Geforce 3 Ti 200 64Mb
Using the Onboard 5:1 Sound
Generic Network Card

Windows XP Professional
(Windows 98SE)
NVIDIA Detonators 23.12 / 27.70
Latest VIA Drivers

Currently I am having problems with Blue Screens of Death
(IRQL_LESS_OR_NOT_EQUAL), under Windows XP which I have been unable to come up with a soultion as yet. Mostly they occur when trying to do any serious work (such as DivXing), and occassionally just when booting up, yet it will play games all day without a single problem.

I have tried reinstalling Windows several times, both with and without VIA Drivers, in order to try and eliminate the problem, but even without any drivers installed (i.e. plain XP installation, with just one of my DivX programs) and I still get these errors. My only guess would be that it is a IRQ sharing problem, since I have about 4 devices (GF3Ti, USB2 controller, and 2 others) sharing IRQ11, but this cannot easily be changed, can it?

And to make this issue even worse, Windows 98SE still works fine, which leads me to believe it is a Windows XP compatibility or configuration issue.

Does anyone have any suggestions ?

Can you try different memory in that machine. Specifically, branded memory.

I haven't got another stick to try at the moment, but I am going to try installing Win2K and see if that also has problems, since I think it would be strange that memory would cause it to fail on XP but not on 98SE. Thanx anyway though