Blizzard has announced on the World of Warcraft website that players can now sign up for a chance to get into the StarCraft II beta. All you have to do is go to Blizzard's Battle.net website to go through the sign-up process and upload your system specifications.

Blizzard has also published an extensive FAQ that should answer some of your questions. Blizzard did not specify when the beta will begin except for just saying "in the coming months."