As John, Keith and others are reporting Virtual PC is now free, the download and full details are here:
Whether Microsoft virtualization technology is an important component of your existing infrastructure or you're just a Virtual PC enthusiast, you can now download Virtual PC 2004 Service Pack 1 absolutely free. Microsoft is also offering the free download of Virtual PC 2007, with support for Windows Vista in 2007.
Get the Most out of Virtualization with Virtual PC and Windows Vista EnterpriseInstall up to four copies of the operating system in virtual machines on top of Windows Vista Enterprise with a single license. Learn more about Windows Vista Enterprise.