We’ve heard little bits of information about Hyper-V Server, the dedicated version of Windows Server 2008 that can only run the Hyper-V role. You can read about it now.
Microsoft says: "Customers who require richer and more robust virtualization features, such as Quick Migration, multi-site clustering, large memory support (greater than 32 GB of RAM), and more than four processers on the host server, should use Windows Server 2008".
Hyper-V server is aimed at branch office server consolidation, VDI (where there is a broker to manage hardware fault tolerance) and test labs.