Well, the sign-ups began a while ago, of course there's no guarantee to get into the beta unless you were at one of their promotional events. But I'd say that the sooner you sign up, the more likely you will get in. The beta signups are on the website
www.warhammeronline.com
I'll say this much about the game, it aims to be much more pvp oriented than WoW, whether thats good or bad depends on your tastes.