Ahuh, well on 10.5.5 the menu bar icon works, but i think that im running the same on the G5 too! Of course i might be wrong, ill check tomorow and let you know!
Do yourself a favor and run software update. Later software versions fix bugs that are present in earlier versions, and they often include security fixes that leave you very vulnerable if you don't install them.
And yes, running a different version than everyone else might always be the problem.