[RESOLVED] Prob w/ ASUS V3800 TNT2 & SMC1211TX network

I'm having framerate trouble when I try and link up certain games (eg. Unreal Tournament). I've got an ASUS AGP V3800 TNT2 w/32Mb and in single player it works fine using D3D renderer. Link it up and the framerate drops to about 2 fps! I've tried just about the latest of everything in my PC (drivers, BIOS, you name it). I thought it might have been an IRQ clash, as PCI slot 1 uses the same IRQ as the AGP slot, but even moving the network card (an SMC1211-TX card) to a different slot didn't fix anything.

I'm completely out of ideas. Anyone else have anything I could try?