How can I block the automatic installation of Windows Server 2003 SP2?
Microsoft has released a blocker tool, which you can download at http://www.microsoft.com/downloads/details.aspx?FamilyId=FC145B0BC148-445A-82BA-9B2F3AEF6E60&displaylang=en. The toolkit contains an executable file, a script, and an .adm template for Group Policy deployment. Each mechanism performs the same modification, which is to create a registry key (HKEY_LOCAL_MACHINESOFTWARE\Policies\Microsoftwindows\WindowsUpdate) and add a DWORD value DoNotAllowSP that's set to 1. Without this key present, the service pack will be delivered automatically starting June 12, 2007. This key will take effect until March 13, 2008, at which point the service pack will be applied regardless of the registry key's presence.
—John Savill