I recently implemented Windows Server Update Services on my network, and I'm pretty happy with the results. I get to control who downloads and installs updates automatically, who just downloads them, and who doesn't do anything. I can also see which computers need critical updates and haven't installed them yet. To top that off, WSUS downloads all the updates to your own server, so all your clients don't have to download them separately and use up all your bandwidth. You can also approve or disapprove updates to prevent them from being installed--a very handy admin tool for bigger networks or small ones that you end up having to run 40-some-odd updates per Windows XP SP2 machine installed.