Microsoft has released Windows Vista beta 2 to the public as part of their "customer preview program." If your computer meets the specs you can download (or request a DVD) with the latest build.
You can find lots of information including System Requirements, details on the different versions, and download from here:
http://www.microsoft.com/windowsvista/getready/default.mspx
As with the Office 2007 beta (actually, more so) remember that this is a beta product. You probably don’t want to run it as your production machine. That being said... please forgive my hypocritical statement as I am composing this blog with Office 2007 beta 2 running on my new production build of Vista beta 2.
Today was day one of running Vista in production and, while there have been disappointments, I am definitely liking what I see. Over the next few days I will post some more of my experiences here and to http://blog.iwkid.com.