Windows Service Pack Blocker Tool Kit
A blocking tool is available for organizations that would like to temporarily prevent installation of Service Pack updates through Windows Update.
Here’s a nice descriptive tool kit to guide you how to take control of WU/MU.
This assumes you aren’t using WSUS as that tool and its associated GPO’s provides all the control you need otherwise.
BTW – make sure you take a moment to view the SBS Theme Song for inspiration.