Spreading around the web is an image of the official limited edition Halo 3 box with three DVDs.
From the image, you can see the disks titled 'Game Disc 1', 'Game Disc 2' and 'Bonus Features'. What's this mystery 'Game Disc 2' you ask? Well, some seem to think it could merely be two parts of the game, or maybe, one for single player and another for multiplayer.
However, TalkXbox is going to add a twist to these rumors by pointing towards the possibility of a map editor being included on the second DVD. Now before you start writing this assumption off, it isn't too far fetched since code relating to a map editor has been found in the Halo 3 Beta source