CoD4: Multiplayer Mode from a single PS3 unit

Hello,

I have CoD4 for the PS3, and for the most part I think it's a great game. My question is based on a feature I saw once in another game. If I hook up two controllers, the game will allow myself and a friend to fight each other. But is there a way for myself and a friend to fight together from the same PS3 unit against the enemy in say a mission (offline)? Also, is there a way that myself and a friend can both fight from a single PS3 unit in the online multiplayer games, like Free-for-All or Sabotage?

If no on both counts, is there a war-based fighting game available for PS3 which has either or both of these features?

Thanks so much.