Here is an example on how to add a program to a user's login items under OSX. I wrote this script for use with an installation program that I put together using a combination of REALbasic, some C++ plugins, and some Applescript.

To use prepare it per the Notes section below. To use it in an RB application just call osxAddToLoginItems(full_path_to_appliation).

(*
    File:       osxAddToLoginItems.applescript
    Author:     G. Tillman
    Project:    PerformancePower Installer
    Purpose:    Script the processing of adding a Login Item under OSX to the 
                User's  Login Items System Preference
    History:    0001-20030109 (got) initial creation
                0002-20030126 (got) improved script.  checks to see if app is alread in startup
                                    items before adding it.
    Notes:      This file is the source.  After saving it do a save as "application", using the 
                same name but w/o the ".applescript" extension.  drag and drop this saved 
                application into the rb project window.
*)

on run {appPath}
    tell application "System Events"
        set thePath to ""
        set foundApp to false
        repeat with lItem in login items
            set thePath to (the path of lItem)
            if appPath contains thePath then
                set foundApp to true
            end if
        end repeat
        if not foundApp then
            (* add it to the startup items... *)
            make new login item at end of login items with properties {path:appPath}
        end if
    end tell
end run