Ben's blog (link below) has an announcement on the availability of Beta 2 for Virtual Server 2005 R2 SP1. Included improvements are:
AMD Virtualization (AMD-V) compatibility Intel Virtualization Technology (IVT) compatibility Volume Shadow Copy Service support Offline VHD mounting Active Directory integration using service connection points Host Clustering technical white paper
Link to Virtual PC Guy's WebLog : Virtual Server 2005 R2 SP1 BETA2 is available for download!