Hallo,
basically - previous versions used LoginItems mechanism for autostart. But, this mechanism has some drawbacks (adding very first item from a third-party app), and also isn't fully functional (for example, hiding of launched apps doesn't work well). Newer versions use launchd (which was already in Tiger, but unusable, because there was no tracking mechanism of user-session and thus the daemon wasn't suitable for running apps with GUI context), but this will be activated on Leopard only (Apple fixed these flaws on Leopard).
Summary: tiger - autolaunch via LoginItems, check whether the app has its record there (Preferences, System-Accounts, LoginItems)
leopard - autolaunch via launchd/launchctl, check the "launch at startup as persistent applicvation" checkbox in preferences, or use "launchctl list" from terminal..
regards,
pc