Re: Trying to make headway into finding the Xid crashes source...
Interesting... my hardware is similar to yours. Relevant items:
Soyo P4S 645DX Dragon Ultra
P4 2.53, 533Mhz FSB
GF 5700 Personal Cinema (@ AGP 4x)
Creative Audigy 2 ZS
FWIW, I enabled AGP write masking in the SBIOS and the problem disappeared. My system is stable with Composite (yeah, I know), RenderAccel, and APIC enabled (although IO-APIC isn't supported by my mobo). It's slightly overclocked too, but I'm not touching the video card's clocks.