Microsoft has released Hyper-V VHD images of the beta releases for Windows Server 2008 R2 Core and Full installations. Strangely, they are RAR files.
These VHD’s will only run on Hyper-V. Don’t worry, you can always install them on a Full installation of an MSDN or TechNet Hyper-V server (to use the local console) or on the free Hyper-V Server 2008. Be sure your host hardware is Hyper-V compliant.