I found this at http://elrath.com I have not tested it and neither do I take any credit for it. As you may have guessed from the quote it is supposed to modify they multiplayer maps to allow for allies.unreal_az has modified the current maps in the game so you can play with a friend against the AI.
It's just a little something to tide everyone over until the extra 10 maps are released and the map editor comes out.
http://deep.phpwebhosting.com/~paradox/upload/maps.rar