Inerrancy

I've been doing a lot of reading for school over the past week, trying to take advantage of my time off and trying to understand the documentary hypothesis of the Pentateuch in its classic (Wellhausen)form. If anyone out there understands it, could you please explain it to me?
What has interested me (and what I have understood) are the chapters about inerrancy and inspiration. We cannot accept only parts of Scripture as inspired; it all works together so well it's either all or nothing. And if it could be partially inspired, who decides what parts? Where do we draw the line? No, if we cannot accept that all Scripture is from God, then we have to let it all go. Once we start to decide based on human wisdom and reasoning what is and isn't from God we make ourselves out to be greater than God, able to judge His words.