DrWho, both the medium res version I posted to the forum and the Pong mod I posted to the dailyduino can VERY easily be modified to take inputs etc. Just put whatever you want in the loop routine (the loop routine is just an example). Because the vertical refresh is interrupt driven you dont have to worry about timing in any code you add. The only limitation is that loop doesnt get very many CPU cycles and the bitmap uses a bunch of RAM.
FYI I havent gotten around to coding the "High Res" version, but I have it worked out how to double the pixels again. It shouldnt take any more RAM than the existing code. If anyone wants to try it I will outline the changes that need to be made.