Microsoft VHD Test Drive Program 

( Quoting ) " The Microsoft Virtual Hard Disk ( VHD ) format is the common virtualization file format that provides a uniform product support system, and provides more seamless manageability, security, reliability and cost-efficiency for customers. 
 Using the power of virtualization, you can now quickly evaluate Microsoft and partner solutions through a series of pre-configured Virtual Hard Disks (VHDs). Users can download the VHDs and evaluate them for free in your own environment without the need for dedicated servers or complex installations. " 
 http://technet.microsoft.com/en-us/bb738372.aspx