Posted Mon, Sep 05, 2011 by Martuk
Getting your name in for selection is easy so long as you have a Battle.net account with at least one Blizzard game attached. All you need to do is head over to your account page and click the Games & Codes section and run through the systems check on the Beta Profile Settings option. Once done, you’ll be opted in for beta selection.
Source: Diablo III Beta Opt-In FAQ