As is customary, Blizzard's first beta for Diablo III - which has now begun - is with employees and family of the company. That probably doesn't include you. But that's OK. You can watch other people play!
There's no non-disclosure agreement covering the beta, so those employees and their families are free to broadcast whatever the hell they want. And they are! At places like this. And this. And this.
Still no exact word on when a beta for us common folk kicks off. Sorry!