Okay, this might be a cooky idea, but can you independently read the input from two different mice plugged into the same computer? I have a craaaazy idea for doing a co-operative game on a single computer that is entirely mouse driven. I think there's a lot of potential there, and I'm pretty sure its technically possible. I have actually played Serious Sam split screen on a PC before, by using two mice and two keyboards... I'm not saying its comfortable, but there exists at least one game in the history of the world that could actually parse the input from two mice at the same time, so it should be possible!