I'm sorry to be a bit late on this but last week Hyper-V was finally released! Our new virtualization solution, as part of Windows Server 2008, will make the server even more compelling in my opinion. And on the topic of Green IT, server consolidation is of course a big aspect. There's tons of material to read about Hyper-V, here are a few good linkshero-hyper-v

Reviews:
ZDNet
PC World
CNN

Hyper-V home page

Hyper-V FAQ

Information about Guest OS support