Mac OS X can download and install software updates from Apple via the Internet. Starting with Mac OS X 10.4 (Tiger), your Mac can be configured to download these updates from your own Mac OS X Server. This can greatly increase update speeds and reduce your bandwidth usage. It can also allow you to limit the updates available to your clients from your server.
Software Update Client Configuration is an application that allows you to set your Mac to use a custom software update server without using UNIX commands or binding your Mac to a managed Open Directory domain.
This software is free to use, but donations are being accepted to fund the purchase of a wheelchair-accessible vehicle for writer Michael O'Connell (of theniceguycomic.com) who has Muscular Distrophy.