Much of the world has been eagerly awaiting Blizzard to announce the beta for StarCraft 2. Today, Blizzard has granted that wish by by announcing that signup has officially opened.
Blizzard has a few pre-reqs that you must complete before you can be officially signed up, and even then you won't be guaranteed to get a spot. First you will have to have a Battle.net account with at least one game attached to your profile. Second you will have to submit your official system specs to Blizzard.
Blizzard wants to get as diverse as possible when testing the game on hardware and as such they will be selecting testers manunally to get the outcome they are looking for. Blizzard hasn't given an exact date for the launch of the beta, although it will be open in a few months.