A KB article (http://support.microsoft.com/default.aspx/kb/950792) has just been posted about problems that people are encountering with installation / uninstallation of Hyper-V RC0.  This is caused by and incompatibility with the Hewlett-Packard (HP) Network Configuration Utility.

If you hit this problem - the KB article tells you how to get things working again.  If you are installing Hyper-V on a HP system it is recommended that you uninstall the HP Network Configuration Utility prior to installing Hyper-V.