At Microsoft's X06 press event, they announced that a new game in the Halo series will be coming out. [i]Halo Wars[/i] is a real-time strategy game set in the Halo universe. Developed by Ensemble Studios (behind the Age of Empires series), the game lets you take command of the UNSC forces and fend off armies of Covenant Soldiers. The game is currently slated to be exclusive to the Xbox 360, but it wouldn't be surprising if the game lands on Vista.
You can check out the official [i]Halo Wars[/i] site right here: http://www.halowars.com/