Exchange Server 2003 support under Virtual Server 2005 R2
I know this is a little late - but as of Exchange Server 2003 SP2 and Virtual Server 2005 R2 - Microsoft is now officially supporting the use of Exchange under Virtual Server:
https://support.microsoft.com/default.aspx?scid=kb;en-us;320220
Woo hoo!
Cheers,
Ben