JUST RELEASED!!!  This is an update to enhance the Hyper-V role's support for processors and virtual machines.  Hyper-V will now support support up to 24 logical processors and 192 virtual machines!!!

Where Do I get the Update?

It's on the Microsoft Download Center and can be downloaded from here: Update for Windows Server 2008 x64 Edition (KB956710)

This update will not be available as a general release through Windows Update due to its specialized nature and the limited number of systems needing it.