I recently upgraded my computer to this:

P4PB 400-FL motherboard
simpletech 512MB PC2700 memory
Visiontek Xtasy 9600 128MB AGP
2.4Ghz Intel Celeron

I first put in the Visiontek video card with the old equipment to do a
benchmark. I then put in the new processor, motherboard, hard drive, &
Visiontek card. I installed a clean install of Windows XP on the new
hard drive. When I benchmarked the system with 3DMark2001, my new
configuration runs slower then my old AMD 1300 system (6475 with 2.4
Ghz & 7426 with AMD 1300). The CPU & memory scores are much higher in
PCMark, so the system isn't running slow overall. I've installed the
latest motherboard 4in1 drivers, flashed to the newest BIOS for the
motherboard, tried the Visiontek drivers, ATI's own drivers, the
omegacorner.com drivers (which failed to install). I've checked the
AGP voltage (1.5v). I tried turning off "fast write" in SmartGart. I
can't figure out what has gone wrong.

The Visiontek manual says the card should use IRQ 10 or 11, but I
don't see a way to force the card to use this IRQ in the BIOS, and
Windows XP won't allow me to disable "choose automatic settings" in
Device Manager and change the IRQ manually (I have admin rights). Can
this one IRQ detail be slowing down the video card that much? Has
anyone come across a conflict with this VIA motherboard and Visiontek
9600 (or is running them just fine)? Any other suggestions? Thanks for
any help.

I bought and put together the same processor and CPU for someone else,
and they score higher on 3DMark2001 with their older Radeon 8500 card.