I just downloaded a new version of Windows Server 2008 R2 64-bit and to my dismay, Dreamspark shells the image out as a .img file instead of the typical and beloved .iso. I looked online to find out what the heck to do with the .img file and found a bunch of sites explaining how to run a command line program (VBoxManage) to convert the .img into a .vdi. The conversion went well but the .vdi did not work when I tried to mount and start the VM to boot to it.
To my delight, I then tried renaming the .img to have an extension of .iso and SNAP! It works. Mounted up the .iso in typical fashion and Server 2008 is now running on my MacBook Pro. I understand Ubuntu is handing out .img files instead of .iso as well. Must be some better compression value or the like (the Server 2008 R2 Standard/Enterprise/Web/Datacenter all in one was only 3GB).