Only 2.5 million of Windows 7 activation keys are available worldwide. The beta will expire on August 2009 (assuming you have the key activated). If not, you’ll only get 30 days of trial (+ a couple more months perhaps with the ReArm trick to extend the trial).
To get your key and download Windows 7 Public Beta, go here.
The server was getting hammered earlier. I ‘ve been getting “Server too busy” error and now Microsoft has decided to actually take out Windows 7’s download/access from the site. The page now says “Windows 7 Beta coming soon!”.