Keef,
I know the P3V4X well. It is the old Apollo Pro 133A Chipset. When you install WinXP you need to also load the
VIA Hyperion 4in1 Drivers for the motherboard.
Also try putting SB Live! in PCI Slot4 and set the IRQ in the BIOS for that Slot to IRQ5. (That PCI Slot does not share IRQs.)
Take Care,
Richard
P.S. That board does not support APIC so give the VIA Drivers a shot before you do the Fresh install on WinXP. I just want to see what happens to your IRQs.