M$ has ended the Public preview of the Vista Beta. So you cant download it anymore.
Also the Public wasnt made available the new build that was released. That was only for Official Testers.
"Get Vista beta 2 before we stop downloads/orders
Update: The program will close on Friday June 30th 2006
In case you weren't aware, we are only providing a limited number of copies of Windows Vista Beta 2 - either download or physical copies - and we're fast approaching the cut-off point.
What this means is - if you want to get a copy, get it now (and I mean now). Visit www.microsoft.com/betaexperience/engb
and either download or order. Because WE WILL BE WITHDRAWING ACCESS VERY SOON. Did I say that loudly enough?"
Came right from one of the M$'s guys blogs. Story here
So sorry you missed out. The only thing you can do now is get it by less than legit means now.