As a result of a query I had about the supportability (or otherwise) of running System Center Virtual Machine Manager (SCVMM) 2008 in a Hyper-V virtual machine, Clive Watson pointed me in the direction of Microsoft knowledge base article 957006, which discusses the support policy for running Microsoft server software in a virtual environment.
For anyone working with Microsoft software on a virtual infrastructure (even a non-Microsoft environment via the SVVP) it looks like a useful article to be aware of.
(and yes, SCVMM 2008 is supported in a VM – both server and agents.)