[Elladan and Elrohir]

As for the Gandalf "no weapon any of you have can hurt me" quote, which was mentioned earlier in the thread: I think he can truthfully say that because of his enhanced power that was granted to him for his return. Apparently, he becomes invincible to weaponry.

Also, to answer another point mentioned earlier, I regret I don't know which one, but Tolkien did write in one of his Letters, "While he [Sauron] wore it [The Ring], his power was actually enhanced..."

And finally to discuss the main point of this topic:

I had always assumed that Sauron was essentially killed by Elendil and Gil-galad as he did the same to them. I still do, though my belief in that isn't as strong as it was. The word "overthrown" appears to be operative ("They overthrew Sauron, though they themselves perished in the doing"), and I take it to mean that they literally overthrew him. Whether they "killed" him or not, he was knocked over and at least temporarily immobilized. It was then that Isildur cut the Ring off his finger.

I don't see how Tolkien could call Sauron "overthrown" if he was still swinging his mace (or whatever) around and killing people left and right, as the movie depicts. I think he was literally overthrown.

My $0.02.