Most people put 2-and-2 together when they heard that Gears of War will definitely run on Windows XP, and figured that Games for Windows LIVE for XP would be forthcoming as well.
For the doubters, VE3D has the word direct from Microsoft that XP support is indeed coming.
Games for Windows – LIVE is the Windows counterpart to our Xbox LIVE online gaming and entertainment network for Windows XP and Windows Vista.
Still no word on when the XP installer will become available. Maybe the latest version of the installer already works! Try it out and let us know :)