The following is specualtory

In January 2004, Bungie began the Alpha Testing phase for its xbx first person shooter Halo 2, 11 months before its launch on november 9th 2004. Halo 2 entered pahse 2, Beta Testing in July 2004, 6 months before launch.

Halo 3 entered in studio testing, the equivalent of a closed Alpha test in May of 2006. By timeline equivalent of Halo 2's, that puts the launch 11 months after May 2006, which is Febuary/March of 2007. While it was specualted Halo 3 might not launch until next winter, the stage of game development points twoard a release date in the first half, if not first quarter of 2007. More on Halo 3's release in September.