If your users are anything like me, they like to install updates they’re not really supposed to. I guess it’s just old fashioned rebelliousness that gives me a tiny thrill when I click to get my updates instead of the ones approved by my system administrator.
As I reminded you in November, you can block installation of SP1 using the Windows Service Pack Blocker Tool Kit from Microsoft. By running an executable or script from the kit, you can stop a machine from installing the service pack for up to a year from when the SP comes out.
Note that all the script or executable will do to your machine is create and set a registry key at HKLM\Software\Policies\Microsoft\Windows\WindowsUpdate with the value DoNotAllowSP (or remove this key if you tell it to allow the SP), so there’s no reason you can’t make the change yourself. The kit also comes with an ADM template if you prefer to do things that way.
According to the download site, the kit “will not prevent the installation of the service pack from CD/DVD, or from the stand-alone download package. This simply prevents the service pack from being delivered over Windows Update.” So it looks like you’ll need to take more advanced steps, or just accept that some of your users might manage to install SP1 anyway.