It’s well known that, with a Windows Server 2008 R2 installation, you can simply add the Hyper-V role to your server, as long as your hardware supports the role. Once the Hyper-V role is added, you can host virtual machines n the server. However, you still have the full installation of Windows running from which you launched the role addition. This is overhead.
You can install the free Microsoft Hyper-V Server 2008 R2 product right onto the bare metal without the full Windows overhead. That said, going this route will require that you either manage Hyper-V from the command line or from a computer that has full installation of Windows Server 2008 R2 or Windows 7. This will allow you to run the GUI-based Hyper-V Manager so that you don’t have to deal with the command line.