Halo 2 is headed to the PC and there is the possibility of it being developed inhouse in Bungie rather than a 3rd party developer doing the port. The PC version will include Halo 2, the bonus maps that came in the Multiplayer Map Pack, and the ability to "build, create, and customize their own multiplayer levels.
So what's the catch.. You need Microsoft Windows Vista, MS brand new OS coming out this year.. hmph.. what a bad marketing ploy..
http://www.gamespot.com/news/6143976.html