GameSpy informed us of an interview they've conducted with Ed Fries, Executive VP of Microsoft's Games Group. Among other things, Ed confirms that Halo will be coming to X-Box. The article also quotes Bungie's Alex Seropian on the future of PC and Mac gaming:

I am really concerned as to how our PC and Mac fans are going to view this deal, Seropian said. Our fans have brought us to this point and are the reasons why we exist. In the short term, especially the Mac fans have a lot of fears about what this might mean. We are still going to make decisions the way we have always made them. It is about what makes most business sense and what is good for the game. In the long term if what our fans want, is to make games that push the envelope of technology and are fun to play. Then there is no question this deal will be awesome for them. But Seropian said the short-term for Bungie is clear. This [deal] gives us a chance to be a premiere developer on a brand new console and to have a huge impact on how that console gets made, he said. It's an opportunity that we were only probably going to get once so we jumped at it.

The GameSpy article speculates that the future of Mac Gaming may not look so bright. However, I have been told by a Bungie employee (who shall be unnamed for now) that there would be no point in making Halo for the PC and not for the Mac. The future of PC and Mac support is the most critical question on the mind of many gamers, and is for now going somewhat unanswered. Only time will tell how this scenario will play out. Until then, I'd suggest that we all try to stick as close to the facts as possible, and avoid unnecessary speculation.