Today Microsoft announced that it was changing it's licensing terms for 41 of it's server applications, so that customers can receive technical support when deploying those apps on Microsoft's Hyper-V virtualization platform, or any validated third-party virtualization platform.
With the new support policies, customers get the same level of product support in a virtualized environment that they are accustomed to with non-virtual (physical machine) environments.
Check Microsoft's updated licensing terms here.
Read more about virtualization at Microsoft's Virtualization Team blog, or VMware's Technology site.
As of the announcement, the only third-party hypervisor that has passed Microsoft's validation testing is VMware's ESX 3.5 update 2. VMware's press release is here.
