I think both your comments on what was happening between Boromir, the Ring, and the Council are right on.
Is Boromir's motivation to bring honor and glory to himself (and maybe be proclaimed King?) or was it to save Minas Tirith with the honor and glory accompanying the completion of such a task being nice, but secondary to the saving of Gondor?
-Kevin
I think his motives are pure enough and patriotic, and certainly likely to bring personal glory to his name. But he doesn't have it yet. He is seduced by the idea of it, and the vision is still a romantic and heroic one. He is not an evil man, only a misguided one.