The only way I can get Fallout 3 to play on my secondary display (a projector) is by running it windowed and dragging that window over to the second display after I start the game. There doesn't seem to be any way to run it full screen on the secondary display...but I've definitely done that with FO:NV and Oblivion (although I can't remember what I did to get it to work, sadly). Is there some .ini line or something I need to tweak in order for this to happen?