First Boot Script

I have successfully used InstaDMG to create images that include createUser and clearReg packages. I have now created a First Boot script to set the computer name, enable ARD and SSH access, set the Start Up disk and enable a Network Time server. I tested it by creating a loginhook in a terminal session on a newly imaged Mac. It works perfectly. I am using an Intel powered iMac and OS X 10.5 My problem is that I do not know where to save this script so that it can be run on the first boot. I am thinking about creating a System Config script which I would use as a post flight script in a payload free InstaDMG package. This would merely create the required loginhook. Will this approach work? Where should I save the First Boot script? Any help greatly appreciated.