Quoting Jeff Alexander blog, via Bink.nu:
One of the most requested applications customers want to see supported on Virtual Server is Exchange. Well today is a good day because we have just announced support for Exchange runnining on Virtual Server. With the release of Exchange Server 2003 SP2 we now support Exchange running on Virtual Server 2005 R2 release. This means you will have to be using Virtual Server 2005 R2 to get this support.
The last I heard is we are 3 weeks away from shipping the R2 version of Virtual Server so this combination of products will be realised very soon.
Check out the web link for more support information:
http://support.microsoft.com/?id=320220