This would not be easy, to say the least, and something gives me the feeling you don't know much about this matter. If a games engine was not created with the intention of supporting split-screen, it would be relatively a lot of work. Not only do you have to make the rendering to support split-screen, but also add support for more than one local player (input, game logic, etc).
There's also the idea about scripting certain games to run twice on a single machine and just having them connect to each other via a script.
That's kinda a hack, but might work if the machine could handle the load of two users at once on the same machine.
I don't see how you intend to connect two games via a script. However, if a game supports network play there is no reason why two instances of that game could not connect on the same computer as most programs can. Just try running OA twice on the same PC, create a server on one game and connect with the other. No script needed. If the game does not support network gameplay, then a script won't help you (no matter the 'magic' you put into it).
By the way, should this topic be in Club Nub or something?
