Take note that Dynamic Memory is only supported if the Guest Operating System is “aware” of Dynamic Memory. At this time, Windows Server 2008 R2, Windows Server 2008 with SP2, Windows Server 2003 with SP2, Windows Vista with SP1 (Enterprise and Ultimate) and Windows 7 (Enterprise and Ultimate). The Hyper-V Dynamic Memory Evaluation Guide has the additional detail, but basically all of the Server SKUs, Standard Edition and above, and the Professional Desktop SKUs support Dynamic Memory.