Mac OS X Server 10.6.7: Disable Apache?
If this is OS X Server (i.e. the server product, not the regular desktop OS), turn off the web service in either Server Preferences or Server Admin.
You could disable the launch daemon.
I'm not an expert with launchctl but the following command should work.
sudo launchctl unload -w /System/Library/LaunchDaemons/org.apache.httpd.plist
Turn off Web Sharing. You might have to restart. There are other ways of doing it also. Keep searching.