Microsoft and Red Hat Cross-Certify to try and get VmWare out of the Datacenter. Red Hat Enterprise Linux 5.2, 5.3, 5.4 has passed certification tests when running on Windows Server 2008 Hyper-V, Microsoft Hyper-V Server 2008 and Windows Server 2008 R2 Hyper-V, Microsoft Hyper-V Server 2008 R2.
Windows Server 2003/ Windows Server 2008 / Windows Server 2008 R2 are validated to run on RHEL 5.4, using the KVM-based hypervisor.