Best 2 Player LAN PC FPS game?

I'm going to my Mom's for the weekend for something near my hometown. I got her a new computer recently so I'm taking my laptop and will try to get a game going with my brother who doesn't have much experience with PC gaming. I'd like to get a LAN game going and although I know he would like CS, DoD and other HL mods...my mom won't have her cable internet connection up until after this weekend on monday and her dialup sucks even compared to other dialup connections (wiring problem I think).

What is the best first person shooter to play over LAN with 2 players? The only one that comes to mind and I have is Serious Sam. Any other good lan coop fps games out there?

Mechwarrior; either cooperatively, or PvP with computer lancemates.