We've deployed Windows 2000 service pack 3 to about 400 PC's
I just copied the extracted service pack to a directory on the server and then created an app object that executed update.exe and used the -u switch to make it unattended.
When the app ran, it just started up, checked everything it needed to check, then backed up the files it was about to replace, then replaced them, then shutdown/rebooted the machine.
It should be noted that once the service pack completed, it took a little over a minute till the machine rebooted itself.
There are other switches that can be used for different methods of deployment.
We'll probably be doing something similar with SP4 once I feel it's safe to install.
Hope this helps
Tony