First, navigate to Start -> Programs -> Administrative Tools -> Services.
Once inside Services, right-click on Automatic Updates, and choose the option for Properties.
In the Properties dialog box, click the drop-down arrow and choose the option for Disabled.
Click on Stop to end the currently running service, and then click OK. Windows Updates are now disabled, and will not require a reboot of the server to go into effect.
Please note that all future critical updates, patches and hotfixes from Microsoft will need to be installed manually once this option is disabled.