Creationism and Evolution

I was going to see a speaker tonight who is addressing the question of how Creationism and Evolution are compatible, but am unable to after all. The reason I wanted to go was not to hear how the two are compatible - of course they are if one doesn't take the Bible literally - but to see if the following issue is addressed:

How can a Christian decide to take the parts of the Bible that conflict with science NOT literally, but maintain that other parts (maybe that science has not yet contradicted) should still be taken literally? Of course it's fine to accept evolution if you think the creation account in Genesis shouldn't be taken literally, but WHY shouldn't it be taken literally? How do Christians determine what parts of the Bible are literal and which are not? As far as I'm aware, there is not guide at the beginning that says, Here, here, and here - these stories are not LITERAL, but here, here, and here - these stories really did happen exactly this way.
It's like people go through the Bible and say, Okay, obviously Jonah didn't actually live inside of a whale, so we're going to take that metaphorically. And the story of the ark? Millions of species couldn't have fit on a boat 450 feet long, so we'll take that metaphorically also. And that the world was created in six days, and the moon gives off its own light, and Adam actually NAMED all the species that have ever existed on the planet... But at what point are we obligated to question the literal interpretation of the plagues on Pharaoh, or the wall of Jericho, or the virgin birth? How do we determine which stories we take literally and which stories we don't?

I think my Dad is still going, so we'll see if this question gets addressed...