Harry posted on our hotline server that xbox.ign.com has an article up stating that the preview code for Microsoft's networking service is now available for developers to download. No word on when this will actually make it into games, but it's progress:

What this means is that the backbone of Microsoft's Xbox online plan can now be tested. Code can be downloaded that will allow developers like Digital Extremes, crafters of the online game Unreal Championship, to test out features like content download, voice, authentication, and matchmaking. With test servers up and running in Redmond, the door is now open for game creators to start really testing out online functionality.

Read the entire article for more details.