zlacker

Brief description from their web site: "Qubes is an open source operating system designed to provide strong security for desktop computing. Qubes is based on Xen, X Window System, and Linux, and can run most Linux applications and utilize most of the Linux drivers. In the future it might also run Windows apps." (http://qubes-os.org/Home.html)

>>greeny+(OP)
In fact, the version in development already runs Windows. The blog has a screenshot showing Windows running in 'desktop mode' (as in, you currently don't have single application windows for the Windows VM).

The extra requirements for this seem to be (ignoring that this isn't yet released) that you're having vt-x support, for all I remember.