Intermittent lag, help me play games!

I have a new computer that stutters during games and I've tested other computers on the network and they don't have the same problem. I even joined the same game servers as my brother's comp to make sure.

I'm stumped. This on a fresh install of XP pro and the games i've tested are half-life mods and wolfenstein enemy territory.

My specs are:
Abit AN8-Ultra
Venice 3200+
Sapphire x800xl
1 gig pc3200 corsair xms
samsung 200gig hd

As per some suggestions in #tech I reinstalled video drivers with no luck.

edit: forgot some things

well take your pc to your bros room and use his connection and then his card, do you have a wireless card if so uninstall it and re install.

btw you have any problems with guru? have you updated the bios 1.5 1.6?

but i think it might be your board i had teh same problem, i think its a shit board.