We have released Virtual PC 2007 Beta. It has support for Windows Vista as a guest and as a host, including 64-bit host support and provides an excellent application compatibility solution. It also has support for hardware virtualization technology from both AMD and Intel and to round things out it has improved performance. All of that for a very attractive price.
P.S. I'm in hiring mode again. If you want to make an impact in the industry in the virtualization space then I have a great job for you. Please contact me for details. Qualifications include prior virtualization and marketing experience and a desire to change the world :0).