Bethesda has written up a handy FAQ detailing everything you need to know about the looming Elder Scrolls Online beta test.
The Elder Scrolls Online promises to be a Pretty Big Deal as MMOs go, and while the ugly failure of Star Wars: The Old Republic is a constant reminder that nothing is carved in stone, if anything is going to be able to shake up the genre (and shake loose World of Warcraft's death grip on it), it's Bethesda's long-running RPG franchise. The closed beta testing will be starting soon and if you're one of the many hopefuls who signed up to take part, here's what you can expect.
The first round of beta invitations will be sent out around the end of March, beginning with small groups of "focused testers" who will take part in scheduled beta events, typically held on weekends, which will run for a limited time and focus on a specific aspect of the game. Beta events will become longer and more frequent as the game gets closer to release, and of course more testers will be added as it goes.
Testers will be selected for each beta based on various criteria, such as a stated preference for a certain type of content - PvP, PvE, that sort of thing - or who live in a certain area or have specific PC specs. An invitation to one event does not guarantee you'll be asked to participate in another, and those who do get the call will be receive an email link to the client, which weighs in at around 20GB - so don't dawdle with the downloading.
I don't know what the odds of actually getting into the beta at this early stage may be, although I suspect they're likely somewhere just south of "zip," but if you're the optimistic sort and want to keep yourself informed, check out the whole thing at elderscrollsonline.com.