First thing first, tell me how illogical the existance of a God is (not religon specific). Oh, try to make this less of an attack and more of a teaching.
Well, here is how I see it.
Throughout human existence, there have been thousands of gods made-up by humans. Some of them became quite well known, such as Zeus, Allah, the Christian God, Ra, Thor...etc, the list could fill a small bookshelf.
So by believing in the god of the bible, you are proposing that all gods have been made-up except for yours, even though there is no way to know for sure which one if the "right one". There is no way to differentiate between made-up religions and the supposed "right one". Does this mean god does not exist? No, however, it does completely destroy the credibility.
Second, the only reason you believe in god is because you were indoctrinated - meaning as a kid Christianity was pushed on to you. You never chose to be a Christian, you were born into it. Had you been raised anywhere else, you would be worshipping a different god. Raised in certain households, you might not even believe in any god at all. Once again, does this mean god isn't real? No but it destroys it's credibility. You believing in god is completely dependant on having been indoctrinated, born into a Christian household.
Third, this:
http://www.evilbible.com/Impossible.htm