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For early access to the social features, you'll need to sign up for Microsoft Connect and complete a survey. Filling out the survey doesn't guarantee you'll get early access, but with thousands reportedly being accepted you'll certainly have a good chance.
You'll need to be armed with some technical information about your console and your wireless network, so be prepared to take a few minutes to grab the required information and fill out the survey. And of course, you have to be from a region where Xbox LIVE is officially supported to get in on the testing.