Challenge to atheists: prove God exists

Okay, this is essentially a reprint of the post below, but that one doesn't show up on Technorati right, and someone (Wade, whose new atheist blog is here, so give him some traffic) commented that the challenge was actually worded a little vaguely. To review, I have had many atheists/skeptics claim that if God really wants us to believe in Him, He ought to give "undeniable" proof of His existence. My contention is that there is no such thing as "undeniable proof". My challenge to skeptics who wish to make such an accusation is to come up with a hypothetical example of what such proof would look like. Remember, this is not just proof that you personally find acceptable (there are already about a couple billion people who seem to have that), but proof that nobody could deny. Either of the following would be permissable:

1: Give a hypothetical undeniable proof for the existence of an intelligent being that created the universe with a purpose in mind.

2: Give a hypothetical undeniable proof of the existence of the God of the Bible. Complete adherence to all facts presented in the Bible is not necessary, but the following aspects must be shown: omniscience, "quasiomnipotence" (that is, absolute power over matter, space and time, but not neccesarily over logical foundations of truth), absolute benevolence, and is the inspiration for (if not the actual author of) the Bible. Actually, it need not be the Bible, one could substitue the Quran or some other Holy Book of a major religion that has a fairly well-defined concept of the deity(s) within it.

I once asked an atheist, "If God pushed the sky aside as though it were a curtain, stuck His head down throught the gap and waved, saying, 'Hi, I'm up here!' would you be convinced that God exists?" He pondered and replied, "No, I'd probably think it was an hallucination." I actually admired him for his honesty.