While it is an inevitability, we might have the first visual proof that shows Halo 3 coming to the PC.  This image, provided by Voodoo Extreme, shows the Microsoft Download Service for their games, but while showing Gears of War, and Zoo Tycoon, they also have a Halo 3 banner.

This has shades of the Gears of War PC boxshot that Microsoft said was a printing thing until the had their, “Here’s Gears of War on the PC” announcement.  I will say that if there is a game that could prove cross-platform play can work, it would be this game.  Especially, if they could get it out Holiday 08, as Halo 3 still has a lot of multiplayer popularity on the 360.  And as always, it would be an extra 1000 gamer points for the achievement whore addicted.