Contributed By: Cliff Hobbs [MVP SMS]
Reproduced from the Microsoft Software Update Services: Frequently Asked Questions web page:

http://www.microsoft.com/windowsserversystem/sus/susfaq.mspx#top

"SUS consists of the following downloadable components:

• Microsoft Software Update Services. This is the server component installed on a computer running Windows 2000 Server inside your corporate firewall. It synchronizes with the Windows Update site to deliver all critical updates for Windows 2000 and Windows XP. The synchronization can be automatic or completed manually by the administrator. When the updates are downloaded, you can test the updates in your environment and then decide which updates to approve for installation throughout your organization. The SUS server component is available in English and Japanese.
   
• Automatic Updates. This component runs on any client machine that you want to keep updated using Microsoft Software Update Services. The Automatic Update component is included in Windows 2000 Service Pack 3 (SP3) and later, Windows XP SP1 and later, and Windows Server™ 2003; it can be easily installed on Windows 2000 SP2 and Windows XP RTM. This component enables your Windows servers and Windows client computers to connect to a server running SUS and receive any updates. You can control which server each Windows client should connect to as well as schedule when the client should perform all installations of critical updates—either manually or via Group Policy and the Active Directory® directory service. Automatic Updates is available in 24 languages."