Wired has some details on How to Get Your Windows 7 Beta 1 on Friday (today) when it's released at noon PST. Course, if none of these work, or you're not one of the first 2.5M people to download it (or get keys, or however it works), there's always bittorrent...
Update 12PST: The page to go to seems to be this one, however, I'm just getting "server too busy". Oh, and I hate myself for being pulled into even wanting to try it.... :)
Update #2: The wired page has been updated with direct ISO links (thanks Oneiros Darren).