Microsoft Knowledge Base Article 327850 contains the following summary:
If you are logged on as an administrator, the Automatic Updates feature in Windows 2000 notifies you when critical updates are available for your computer. You can also specify the schedule that Windows follows to install updates on your computer. The Automatic Updates feature replaces the Critical Update Notification feature (if it is already installed). The Critical Update Notification feature no longer offers critical updates. This article describes how to install and use the Automatic Updates feature in Windows 2000.