UPDATE: The below was written in early 2007. Approximately two months before release, Bungie announced that Halo 3 will feature cooperative play via split screen (two players per box) as well as system link and Xbox Live (four players per game). In a four-player game, the host players the Master Chief, and the other players are the Arbiter and two other Elite warriors.

Any combination can be used; four players can use separate consoles over XBL or system link; two players can share a box and connect to players on one or two other separate boxes.

At this time this is unknown. Supposedly such a feature was removed from Halo 2 near the end of the development cycle. It is not known if this is a feature Bungie intends to reintroduce with Halo 3.