Bungie Studios, along with a Microsoft Game Studios, is currently working on porting Halo 2 for use on the Windows Vista operating system. No Mac or XP version is planned as of now.
It has however been confirmed that there will be a map editor that will be made by Microsoft (in cooperation with Bungie Studios) and packaged with the game. The map editor will include the same programs as previosuly used in the Halo Editing Kit (HEK). These programs are Guerilla, Sapien and Tool. The full extent of the map editor's capabilities have not yet been made available.
Halo 2 Vista will have free online play through Windows Live, with the ability to send messages to Halo 2 Xbox players on Xbox Live, but no PC-Xbox gameplay is available. This is at least partly due to the difficulty of implementing crossplay between the Windows Live and Xbox Live gaming networks without problems. Bungie has also stated that there will be some "very compelling reasons" to purchase a paid Windows Live account (possibly premium downloadable content, lagless 16+ player matches, and exclusive gametypes/maps), even though basic online play has been confirmed as being free of cost.