- Type battle.net into your browser (no typos) and it will go to the secure battle.net site appropriate to your region.
- Enter your account info.
- Under Manage My Games, choose Add or Upgrade a Game.
- Enter the Beta Key provided in the email where it says Enter Game Key.
- Press Add Game.
Account thieves are sending out phishing emails all the time -- we get several tips a day. And with SC2 beta actually beginning, the Cataclysm beta scams are sure to increase. So you need to be careful of any official looking email you receive. Always navigate to the site yourself to check things out and remember that Blizzard will never ask for your account information in an email.
If you do determine that an email claiming to be from Blizzard is not legit, forward it to firstname.lastname@example.org. Blizzard has more about identifying phishing emails at this link.