Microsoft has released a tool which helps you in blocking the installation of Windows 7/Windows 2008 R2 Service Pack 1 through windows Updates. You can download it from here.
This download contains three files.
1. SPBlockingTool.exe — A microsoft executable
2. SPReg.bat — A batch script
3. NoSPUpdate.ADM — A ADM file to use with GPOs
The installation of service pack 1 through Windows Update can be stopped with one of the above above given tools. If you plan to use the executable, you need to pass /B switch to it to block the installation and /U switch to unblock the installation. Similar functionality can be achieved with BAT script also. It helps you to run against remote system as well. Third approach is using the ADM file in your Group Policies. This GPO procedure is very straight forward and like using any other ADM file.
Irrespective of approach you use, it creates a key value name “DoNotAllowSP” and sets it to “1” under HKLMSoftwarePoliciesMicrosoftWindowsWindowsUpdate registry key to block the installation. It deletes this newly created key when you instruct it to unblock the installation restriction.
Hope this helps you.