ThetaSigma

You will need to take ownership of the key before Vista will allow you delete it. The ownership of registry keys work exactly as they do with files and directories...

Start RegEdit -> Right-click -> 'Permissions' -> 'Advanced' button -> 'Owner' tab -> click your user name -> check the box 'Replace owner on sub-containers and objects' -> click 'Apply' -> close the open window -> and in the smaller window, give 'Full Control' to the 'Users' group -> click Apply -> close the Permissions window and delete the key

You can delete just about any key in the registry using this method, regardless of whether or not it is in use...but be extremely careful of which keys you take ownership of.