Do yourself a favor and read this Talk Origins article right now. It encapsulates everything I was trying to say about the creationist mindset in this post, but so much more effectively that I weeped little tears of joy at having found it.
To summarize briefly, there exists in the minds of YECs a demon who opens the door to the mind to allow YEC-friendly information in, and closes it to keep contradictory information out. Therefore, YECs are utterly convinced of their position, because they never become aware of the contrary evidence! Further, efforts to sway committed YECs will be fruitless, because they simply will not hear what you say. All that gets through is the information (factual or not) that supports their position.
I haven’t done the article justice, of course. Please read it!