There is a good source of Virtual Server and other product related information on the CEC report website which has been produced by Microsoft to establish a common set of guidelines and requirements that each infrastructure server must meet.
The main site has details for this year and 2006...for 2006 and Virtual Server in particular there is this statement "To help customers improve the utilization of hardware resources, all server products will support Microsoft Virtual Server 2005. Each product must be capable of running from within a virtual instance." There are a few exemptions which have been listed as well.
I’ve been asked what our plans are for VS2005 a number of times recently; there are some good answers to be found here.