As of this morning, a beta version of VPC2007 is now available to the public. Head on over to Microsoft Connect and pick up a copy (look for available connections - the VPC beta program should be listed).
What does VPC 2007 give you?
Well, for one, it adds Vista as a supported host *and* guest.
It's also got hardware assisted virtualization, so if your processor supports VT or Pacifica extensions, virtualization will run significantly faster.
This comes with Mikey's seal of approval, so seriously - if you're running Vista as a host or a guest, you need to check this bad boy out.