Hey i found a simple code to add that makes it become multiplayer. I tried it and it does work. I used the techdemo level and there are some minor glitches but other that that it works. Although it is a tutorial, all you have to do is copy the red text to your main script and do what it says. IT IS SO EASY, A CAVEMAN COULD DO IT. lol. This is what i use for my multiplayer games.
click here