@Tom_Wood: it depends on what kind of license you are trying to install. An OEM license, enterprise license, or retail licenses will all work. MSDN also works.
Dan Stolts "ITProGuru"
Dan Stolts (The "ITProGuru") is a technology expert who is a master of systems management and security. He is proficient in many Microsoft products especially in the server area (Windows Server, System Center, Exchange, SharePoint, Virtualization, Etc) and holds many certifications including MCT, MCITP, MCSE, TS, etc. Dan is currently specializing in System Management and Security and is also very passionate about virtualization technologies. His primary blog is located at http://itproguru.com. Dan is and has been a very active member of the community. Founder of Virtualization Group Boston, founder of North East Leaders and serves on many IT Community group boards including Boston User Groups. He is a believer in social networking and can be reached on twitter @ITProGuru. He has participated in many non-technology community groups such as: Rotary Club, Lions Club, local Chambers of Commerce and is a mentor for the local high schools. Dan is an enthusiastic advocate of technology and is passionate about helping others. Dan's lifelong passion has been and continues to be to help and teach others!