Signups have begun for the Skyrim DLC, Dawnguard Beta. You can sign up via the Elder Scrolls website.
Users must enter their details and answer questions about their Xbox 360, as well as their characters in Skyrim. Users must also be registered on the Elder Scrolls forum.
Selected users will recieve a code to download Dawnguard (for free) ahead of the rest of the world. Dawnguard is stated to cost 1600 microsoft points on release.