A great new feature of Windows 7 is Windows Virtual PC, the next version of Virtual PC 2007. It has all sorts of advantages like dual-core and USB support.
You can use your existing Virtual PC vhd's in Windows 7. But after a while I got tired of some driver issues and reverted back to Windows Vista, and Virtual PC of course. When booting the vhd it made Virtual PC crash right after the login box. The reason for this are the Integration Components/Virtual Machine Additions which are obviously incompatible between the platforms.
An easy fix is to boot in Safe Mode and disable the “Virtual PC Integration Components Services Application” service. After rebooting you can uninstall them.
koning53