Possible ways/solutions for making a 2-player game?

Looking at making a game for GGJ coming up this weekend, and my team is thinking about making a multiplayer type of co-op game. We've done this a lot in the past, but we usually just have two people playing on the same computer/keyboard, which works great if its a simple game with only a few buttons, not so great on something like a FPS. So my question is, what kind of options are there for getting two laptops playing together on the same game?

I've looked into SmartFox, which looks like it could be ideal, but I don't have really any experience working with networking, and I haven't really found anything that would clue me into how hard it would be to figure it out...

Well, one thing, when I tried to use smartfox, I had to go into its code and change the port, because the one it sets as default didn't work... Have you tried that?