The last time I looked there was only a Trial Version of Virtual Machine Manager 2008 R2. It is now possible to download the full version of the product from TechNet Plus and MSDN Subcriber Downloads.
If you have previously installed the Trial Version, uninstall VMM2008 R2 with the Retain Data option and reinstall the software. It will only take you a few minutes.
The next stop will be not be until 2011.