I don't think it is a PCI IRQ problem. This is what I have:
0: 5277376 XT-PIC timer
1: 6152 XT-PIC i8042
2: 0 XT-PIC cascade
5: 20092 XT-PIC uhci_hcd, uhci_hcd, eth0, EMU10K1
7: 53522 XT-PIC libata
9: 0 XT-PIC acpi
11: 318353 XT-PIC nvidia
12: 68695 XT-PIC i8042
14: 520 XT-PIC ide0
15: 38827 XT-PIC ide1
which if I am correct has IRQ 11 for only Nvidia. Of course I have no more Xid's anymore thank god, but that is only since I hardcoded AGP to 2x instead of 4x
and turned off 'AGP Fast Wires'. Altought IRQ sharing might still be a problem cause my system intermittedly crashes when I plug in an USB stick (and its irq is shared if I read this table correctly).
I am no linux expert though, just telling my experiences.