Oof.  It was a while ago, but you know, I think it was figuring out how to do rigid bodies at all that stumped me.  I know it's possible because I've seen animations of dominoes falling...  I think those might have used the game, engine, does cloth simulation work in the game engine?

Edit: aha, http://wiki.blender.org/index.php/Doc:Manual/Physics/Rigid_Bodies