A couple of weeks ago a whitepaper containing a support statement for using MOSS 2007 and WSS 3.0 in Hyper V has been released:
Using SharePoint Products and Technologies in a Hyper-V virtual environment
Important Points covered in this paper:
SharePoint Products and Technologies is supported in a Hyper-V environment. Extensive testing was done to confirm that all the functional aspects of Windows SharePoint Services 3.0 and Office SharePoint Server 2007 have the same behavior on a Hyper-V virtual server as they do on a physical server.
Support for third-party hypervisor technology
Deploying SharePoint Products and Technologies is supported on hypervisor technologies that are certified by Microsoft through the Server Virtualization Validation Program (SVVP) (http://go.microsoft.com/fwlink/?LinkId=125649&clcid=0x409).