Bethesda is taking 'applications' for Beta testers of the upcoming Dawnguard DLC.
1.) This is only for Xbox 360
2.) You must have a registered forum account with Bethesda and the e-mail addresses must match.
If you get selected for the Beta, they'll give you a code to download the DLC for free when it's finally released this summer.
Here's the link:
The Elder Scrolls | Dawnguard Beta
Note to Mods: I posted this here instead of the Skyrim forum due to the fact that this is an Xbox-only Beta.