http://download.windowsvista.com/preview/rc2/en/download.htm

If you want to test the final beta release "Release Candidate 2" of the next Microsoft Windows operating System Vista here is your last chance. The public download should only be available for a few days. The download is an ISO image you must burn to a DVD.

I am running Windows Vista betas on a few machines including a TabletPC and really like it but I am always making sure to back up data so if things go bad I am not losing anything.