Fallout 3: Operation Anchorage is out now!
Currently the only way I see to get it is through the Games for Windows Live! marketplace clients, which you download from their site.
It is 800 points, or $10.
You buy it through the application and it downloads... I will update shortly with how easy and smooth it is to get it working. The directions state it is all automated and FO3 will find it without any hassles. We shall see.
I gots one of them high powered gaming computers with an EVGA GTX 480 video thingy and a Q9550 processing device and also one of them Windows 7 64 operating programs with 4GB of some Corsair 1033 DDR2 ram.
Steam, Xbox Live and PSN: StingingVelvet