http://download.microsoft.com/download/e/e/c/eecf5d44-9a88-43d8-afdb-d2ab82be035c/R2_License_Guide-O... has more on physical and virtual setups. Weather these are strict guidelines of not is another question. We talked at length with or licensing rep, and they talked with MS to confirm things for us.

But if I am understanding you all correctly you are saying - Buy Windows 2008 R2 Datacenter, run it and all virtual OS's as VMs'. Or Buy Windows 2008 R2 Datacenter, run it on a physical box with VMware/XenServer installed and running the VM's.

We brought 2008 R2 Datacenter for the unlimited Windows Licenses we can run in a Virtual Environment, We installed Windows 2008 R2 Datacenter core on the physical box, added Hyper-V, and moved all of our VM's to this box, plus add new ones as we needed. From the guide we understood MS wanted us to buy Datacenter and then run the VM's on the box that has Datacenter installed on it.

So that begs the question what is "one physical operating system environment" or POSE