Beta1 of Windows HPC Server 2008 (aka Compute Cluster Server) has just been released (Nov 2007). The product consists of a unique Windows Server 2008 edition intended for deployment in compute intensive "Beowulf type" High Performance Computing clusters. Included are deployment, operations and scheduling services as well as libraries for development of "cluster aware" applications.
HPC is just one option for parallel computing solutions and specifically intended for localized high bandwidth, low-latency, deployments.
Please also see the following sites:
1. Windows HPC Community: http://WindowsHPC.net
2. My blog: http://blogs.msdn.com/philpenn
3. Product web: http://www.microsoft.com/hpc