Semi-n00b Questions

Hi everyone, I've used InstaDMG images that a cohort of mine setup and it works great; a real time-saver! I am now in charge of keeping the images we have made up-to-date as well as making a new image based on a 10.5.6 retail disk. The main question that is bugging me is how to stay on top of the updates from Apple. If I start today with the 10.5.6 base retail disk I can install it on a machine or drive and then hit Apple's software update server and see what I need to download and also in what order. I don't mind doing this, but if I am not always cognizant of new updates and their order I lose all practicality of making modular images. Does Apple or a third party publish a list of the updates for a specific OS/build and then the date they came out? Like a MacTracker, but for updates. There have been many great posts on here that I have read thru, but any links to an InstaDMG walkthru or tutorial(s) would be very helpful. Thanks in advance to all who respond.