Duck 1: An atheist is simply someone who lacks a belief in God. Skepticism is a questioning mentality.
I'm agnostic, I neither believe nor disbelieve the existance of a god. Under your definition, I am also an atheist, as I lack a belief in God. And as I discussed with Snoopster, Skepticism in the theological sense, is doubt as to the existance of God or gods, basicly an agnostic who leans toward atheism.
Duck 2: Replace God with Santa Claus. I don't believe in God any more than you believe in Santa Claus. I'm an atheist, and if the majority of people believed in Santa, you'd be an 'asantaist' or something. This has nothing to do with how sure we are, as few people would not admit they're wrong if something proved to them, by their standards, that they were. You suggest that to be an atheist, you'd have to deny that God exists even if he proved he does, which demeans atheism and is just plain wrong.
No, what I was saying is that to someone with true faith, no evidence you could give would be enough to convince them God doesn't exist. And to a committed Atheist, no proof would be enough to convince them of the existance of God. They are religous extremes. They are extremely rare in real life, as most people have some doubts in their belief (or lack there of).
As for the question of belief, there is no way to prove or disprove the existance of God. Take the question that my religion teacher liked. What caused the Big Bang ? And if you know, what caused that ? Or caused the thing before that ? Keep going back and sooner or later, you reach a point where no-one knows. A person who believes in God would believe God started it. An atheist would believe it was something else. As there is no proof one way or the other, the person would have to believe their view. The atheist would BELIEVE there was no god. To accept without evidence.
It is one of the things Lini is for, taking the blame. She usualy deserves it even if I don't know how.