Microsoft Virtual PC 2007 has been released and its free like 2004 was. Microsoft is marketing it as a means of compatability for documents and programs. With all of the programs that don’t work in Windows Vista, now with an older version of Windows you can install it on Virtual PC and run the programs within it.
It looks like all they have done to the program is add compatability for Windows Vista, made it look a bit prettier, and maybe some bug fixes.
You can download it here from Microsoft.