i don't know if this will help you, but i'll share my 2¢ anyway:
the best thing to do might just be to let Apple Software Update check for you. if you're missing any security updates, or other OS updates, it should find them for you. Also, there's nothing wrong with running it after it completes an update and reboots, as some updates may require "prerequisite" updates prior to installation.
Good Luck [img]smile.gif[/img]