Hey Mark, about your Gollum: He is not evil; he just has an evil fate, I think. Mark, what would you have became like if you had murdered your friend (blinded by uncontrollable lust), you had been kicked out your home and retreated to the mountains, lived many, many years in lonely dark caves. What would you have eaten, if not goblins (and fish)? Stone?
Anyway, I´ll continue. Your dearest thing and only "memento" of the past had bounded itself to your mind and you have became addicted to it. You probably know that it's hard to be addicted to something; the lust is not stopped by just saying: "you wicked ring! Leave me alone!", as Gollum did. Well my main point was that it was his "fate", all the things that had happened to him, that made him evil.
The same way we can think about Boromir and Éowyn: they did their "bad deeds" because of what had hapened to them, somehow. (Well I think it's quite self-evident and mentioned here before.)