You can now download pre-prepared VHDs
Good news. I've just noticed the launch of the "VHD Test Drive Program". In a nutshell, this is a capability to be able to download evaluation enterprise software pre-configured in a Virtual Hard Disk (VHD) to run under Virtual Server 2005 R2.
Take a look here for more information. I just took a quick peek and there's SQL Enterprise Edition 2005 SP1, Windows Server 2003 R2, Exchange 2007 Beta with Live Communication Server 2005, and ISA Server 2006 Standard Edition. The download centre itself can be found here.
The press announcement can be found here.