I regularly get asked about our licensing and support for running SharePoint on virtualized environments.  Till now, my answer has been that we support on Microsoft virtualization technology ONLY. 

Today we announced that SharePoint 2007 SP1 will be supported on other 3rd party virtualization technologies once they get certified through our Server Virtualization Validation Program (SVVP).

Details at http://blogs.msdn.com/sharepoint/archive/2008/08/18/update-on-virtualization-support-for-sharepoint-products-and-technologies.aspx