I would like to install TMG 2010 for an SBS 2011 installation. I only have one physical server. I'd like to know if the SBS premium add-on windows 2008 R2 license can be installed on a virtual server inside the SBS 2011 installation, and be used as a TMG server.
DO NOT INSTALL HYPER V ON TOP OF SBS! YOU WILL BREAK THINGS!
With that said, you may use Hyper V in conjunction with SBS, but you must install Windows Server Standard on the bare metal and only enable the Hyper V role on it. Once this is done, create a virtual machine for SBS and another virtual machine for Windows Server standard. That second virtual machine is where you should install TMG (and only on that second machine. Installing on SBS would be a no no as it only supports 1 NIC).
You would need the following licenses (plus CALs) in order to be legit with this: