Hyper-V RC1 available on Microsoft Download Centre

Windows Server 2008 x64 Hyper-V RC1 Update - KB950049 This is the Hyper-V RC1 package for Windows Server 2008 x64. This package must be installed on Hyper-V server’s (physical machines).  It includes the Hyper-V Server components for Full and Core installs, the Hyper-V Integration Components for Server 2008 x64 (see note below for RC1 improvements […]

Windows Server 2008 x64 Hyper-V RC1 Update - KB950049
This is the Hyper-V RC1 package for Windows Server 2008 x64. This package must be installed on Hyper-V server’s (physical machines).  It includes the Hyper-V Server components for Full and Core installs, the Hyper-V Integration Components for Server 2008 x64 (see note below for RC1 improvements over RC0) and the Hyper-V Management Components for Full Windows installs.
Note This package is permanent.  Once installed, it cannot be uninstalled.  So you can’t got back to RC0 or Beta after installing RC1.

Windows Server 2008 x86 Hyper-V RC1 Update – KB950049
This is the Hyper-V RC1 package for Windows Server 2008 x86. This package includes only the Hyper-V Management Components for Full Windows installs and the Hyper-V Integration Components for Server 2008 x86 (see note below for RC1 improvements over RC0)It does not contain the Hyper-V Server components, Hyper-V is x64 only!
Note
This package is permanent.  Once installed, it cannot be uninstalled.  So you can’t got back to RC0 or Beta after installing RC1.

Hyper-V Management For Windows Vista SP1 -KB949587 
I highly recommend John Howard's 5 part post on Hyper-V Remote Management.
Windows Vista SP1 – x86 Update
Windows Vista SP1 – x64 Update

Key Updates to be aware off

  • Integration Components For Windows Server 2008 guest’s included in Integration Services Setup Disk.
  • New Graphics for Hyper-V Manager and Virtual Machine Connection – including a “Now” icon in the snapshot pane.
  • Pv4 Address Migration - when creating a new Virtual Network bound to an adapter with a static IPv4 address the IPv4 settings are migrated to the new virtual adapter

Source:→ Microsoft