I think many people will think your still not running a windows 2008 server R2 with SP1. Well I found a server yesterday actually with out Service Pack 1. And I was not able to install this also. After some searching i figured out you have to do some steps to resolve the problem.
when you have done this it could be possible that this services won’t stop (it may be stay in the stopping mode)
When this happens you have to find to correct service in the TaskMgr. You have to kill this svhost.exe process (many other services will stop also but they will start fast again.)
As tip i can give you to open an second CMD window.
After killing the process you need to hit on Enter directly so the folder Download renames to an other folder.
After you have done this run the System Readness Update Tool: http://support.microsoft.com/kb/947821
When you have done this. you can try to install Service Pack 1 of Windows 2008 server R2