Virtual PC 2004 has been available for free for a while. Now the updated version (that also support 64-bit windows) is available:
Virtual PC 2007 page:http://www.microsoft.com/windows/products/winfamily/virtualpc/default.mspx
The Virtual PC 2007 download:http://www.microsoft.com/downloads/details.aspx?FamilyId=04D26402-3199-48A3-AFA2-2DC0B40A73B6&displaylang=en
And if it's needed, the Virtual PC 2004 SP1 download:http://www.microsoft.com/downloads/details.aspx?FamilyID=6d58729d-dfa8-40bf-afaf-20bcb7f01cd1&DisplayLang=en
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.