Yeah, if the game has been published at all it's free game, and even some that haven't been, like the homebrew mentioned above (Or that Sonic Crackers mix). The only exception is when it comes to liscenced music, like EA Trax and the like. As long as the music is specifically from the game and wasn't already borrowed, you're good. Anyone feel free to correct me if I'm wrong, but as far as I know, those are the rules game wise.