I think it would be a bit confusing to put the "create a game" window on the left side when the button is on the right side. Also i think there would be too much stuff on the screen then. It might be
an option to put it on the right side, so when someone clicks the "create a game" button, it grows larger and shows the game options while the other buttons vanish (once you choose to create an own
game the "play with a friend" and "play with the machine" button become obsolete anyways.
Have another badly done mockup:
http://i52.tinypic.com/5f57au.jpgThat way, you would need only two windows in total.
Also, I made background of the lobby opauqe (is that the right word?). I think it's more clean that way. Doesn't look as cool though. Dunno about that.
Also also, I wrote "Select a game" on top of it. I think that clarifies things.