Hyper-V RC1 (KB950049) is available on Windows Update
Update: 26th June 2008. Hyper-V RTM is now available. RC1 is pre-release software.
The RC1 release of Hyper-V (KB950049) hit Windows Update yesterday. For more information on Hyper-V RC1 and some FAQs, take a look here.
Cheers,
John.