Halo 3 Four Player Co-op Strongly Hinted At by Microsoft Exec.

Major Nelson interviews MS corporate VP Jeff Bell. At the end of the interview (4:29 mins in), Jeff Bell talks on how he loves to play the previous Halo games in 2-player co-op, and that he is excited about Halo 3 because he can now play co-op with all three of his sons instead of one.