Virtual PC 2004 Service Pack 1 is now offered as a free download. From the webpage:
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.
Hopefully this will further increase the adoption of virtualization technology. I can’t wait for VPC2007 for it to support for hardware virtualization, like Virtual Server 2005.