List of VHDs on Microsoft VHD Test Drive site

This is where you can download pre-built Virtual Hard Disks, containing Microsoft OS’s and Server Applications like Exchange 2007.
Windows Server 2008 Standard Ed. x86 (full install)
Windows Server 2008 Standard Ed. x64 (full install)
Windows Server 2008 Enterprise Ed. x86 (full install)
Windows Server 2008 Enterprise Ed. x64 (full install)
Windows Server 2008 Standard Ed. x86 (core install)
Windows Server 2008 Standard Ed. x64 (core install)
Windows Server 2008 Enterprise Ed. x86 (core install)
Windows Server 2008 Enterprise Ed. x64 (core install)
Exchange Server 2007 SP1
Windows Server 2003 R2
System Center Configuration Manager 2007 R2
Office SharePoint Server 2007
Forefront codename "Stirling"
System Center Essentials 2007 SP1
Windows Vista

All of the Windows Server 2008 VHDs are designed for Hyper-V, so you’ll need to run them on that platform. Exchange Server, Windows Server 2003 and below (on the list) are designed for Virtual Server 2005 R2 SP1, and the Vista VHD is designed for Virtual PC 2007.