Microsoft has just announced that they have officially released System Center Virtual Machine Manager 2008 R2 SP1, the version of System Center Virtual Machine Manager you need to be able to take advantage of all the cool new stuff in SP1.
System Center Virtual Machine Manager 2008 R2 SP1 supports the new features of Windows Server 2008 R2 SP1:
Dynamic Memory: Windows Server 2008 R2 SP1 Hyper-V supports Dynamic Memory enabling customers to better utilize the memory resources of a Hyper-V host. VMM 2008 R2 SP1 allows administrators to create and deploy Virtual Machines onto Windows Server 2008 R2 SP1 Hyper-V hosts and will report on the memory currently in use for these VMs where Dynamic Memory is enabled. Using Dynamic Memory for supported VMs allows for more efficient utilization of memory, with consistent performance, and higher consolidation ratios.
Microsoft RemoteFX: Windows Server 2008 R2 SP1 introduces a new set of end user experience enhancements with Microsoft RemoteFX. VMM 2008 R2 SP1 allows administrators to create and deploy Virtual Machines with RemoteFX enabled to qualified Windows Server 2008 R2 SP1 Hyper-V hosts. This enables a rich, local-like desktop environment over the network.
PS: It is a 3,5 GB download but it will allow you to do an upgrade next to a new server install. There is no separate service pack available for download.