Lion Server can provide software updates to clients that run OS X Lion, Mac OS X v10.6, and Mac OS X v10.5.
Lion Server uses a single URL which redirects to a separate catalog for each version of Mac OS X:
...where su.domain_name.com is replaced by the fully-qualified hostname of the Software Update server and 8088 is the default port for the Software Update service. If you change the port number for Software Update in Server Admin, you will need to change the port number in the URL to match.
You can point clients to your Software Update server by creating a Software Update payload in Profile Manager, by managing Software Update preferences in Workgroup Manager, or by using the following command directly on client computers:
sudo defaults write /Library/Preferences/com.apple.SoftwareUpdate CatalogURL URL
Replace URL with the URL of the Software Update server, including the port number and catalog file, as described above.