Q. Can I mix Hyper-V Server 2008 R2 and regular Windows Server 2008 R2 Enterprise Edition installations in a single cluster?

A. At the current time (Beta, build 7000) there's nothing to stop you from clustering Hyper-V Server nodes and normal 2008 R2 Enterprise nodes together in a single cluster, however this would limit you to only being able to have Hyper-V resources since that is all Hyper-V Server supports as a cluster resource. At actual release time this may change. The restriction would be that nodes in a cluster have to be running the same type of installation, Full or Core, so to mix Hyper-V Server 2008 R2 (which is based on Core) with an Enterprise 2008 R2 installation, the Enterprise 2008 R2 installation would also need to be a Core installation. If the installation types don't match the cluster would fail validation.