Microsoft (as promised) has released Virtual Server 2005 R2 for free and you can immediatly start to download the package (it's really a must to have).
The first thing that I've observed is the big improvement on supporting Linux-based operative systems, one of the lacks of Virtual PC and the previus version of Virtual Server. Sound good... 
P.S. special thanks to VMWare for the fight on the virtualization market launched in this period... a bit of merit for this free release I think that comes from them 