Nick White at Microsoft’s Windows Vista Team Blog has the Virtual PC 2007 news:
Virtual PC 2007 Beta is now available as a free download from connect.microsoft.com. Virtual PC 2007 is optimized to work well for Windows Vista as both the host and guest OS. This version works with both 32-bit Vista and 64-bit Vista as the host operating system as well as Windows XP and has improved performance including support for hardware virtualization technologies from AMD and Intel. So now you have an easy way to try out Windows Vista, even if you are reluctant to replace the OS on one your existing PCs; or if you have already taken the plunge you can spin up a legacy operating system in a virtual machine on your Windows Vista machine.