For those of you not familiar, there is a group of Christians called "Presuppositionalists" some of whom claim that one must presuppose the existence or non-existence of God and interpret all evidence in light of that assumption (rather than examing the evidence to reach a conclusion).
There is also another sect of presuppositionalists who claim that one must presuppose the existence of God -- particularly the Christian God -- In order to use the rules of logic. To get an idea of their argument, I recommend this webpage, which provides the clearest statement of their position I have come across.
Recently, the TV show "The Atheist Experience" had the author of that article on the show for a fairly thorough debate of his argument that logic depends on God. It's great if you want to see the Christian apologist take a whooping, but it is also pretty deep, so I would recommend reading the article linked above before watching it.