Note: The Screencast about the free Microsoft Hyper-V Server 2008 is available here
We have already demonstrated in one of our screencasts how to install Windows Server 2008 Hyper-V
There are many cases when you have already Hyper-V running on a Windows Server 2008. The first question which you have to answer in such cases is what version of Hyper-V are you running on that server. It could be the Hyper-V Beta (6.0.6001.17101), Hyper-V RC0 (6.0.6001.18004), Hyper-V RC1 (Hyper-V RC1 - 6.0.6001.18010), and of course, there is a chance that you are running Hyper-V RTM version (6.0.6001.18016).
You will need Microsoft update for Windows Server 2008 (KB950050)
In the following Screencast, you will see how to upgrade an existing installation of Hyper-V to Hyper-V RTM version.