Finally they are releasing a public beta . Check it out, it's for everybody, apparently.

"Windows Vista Beta 2 Customer Preview Program
Windows Vista Beta 2 is now available for you to install, test, and enjoy. Here's the information you need to try it now.

Evaluate Your Current PC
Run the Windows Vista Upgrade Advisor beta to help get your PC ready for Windows Vista.
System Requirements
We recommend that you consult the Windows Vista Capable and Premium Ready PC specifications for system requirement guidance on running the core experiences and advanced features of Windows Vista.
Get Windows Vista Beta 2
Windows Vista Beta 2 is available as a download or on DVD. It's time for clarity—try it now!
Windows Vista Beta 2 Resource Center
Once you have installed Windows Vista Beta 2, be sure to visit the Resource Center to download the Windows Vista Product Guide, find anti-virus software for Beta 2, and discover more information that will help you get up and running quickly."

Please let us know if you try it.