I'm no licensing expert but I found this article on Licensing rights for the various Microsoft Server versions with it comes to Virtualization and wanted to share it with the community. Hopefully it will help!
http://www.microsoft.com/licensing/about-licensing/briefs/virtual-licensing.aspx
If you do have any virtualization or other licensing questions I would highly recommend you reaching out to a Microsoft partner that has a Licensing professional on their staff to help answer your questions and help you pick which licensing option is best for your environment.