Via IGN
"Tired of hearing people brag about being in the Diablo III beta? Well you can finally try it for yourself this weekend. Starting on April 20 at 12:01 p.m. PST and running until April 23 until 10:00 a.m. PST, you'll be able to play all of the five classes up to level 13. All of the content can be played alone or with friends over battle.net.
To learn more about how to participate (and download the client right now), check out the official post on Blizzard's site. For more on Diablo 3, check out IGN's wealth of coverage."