I once had a deeply religious girl in high school (a Science Olympiad member, specializing in biology events of all things!) ask me how I could possibly be atheist and still be moral. To her I responded by saying, as an atheist I believe we have one life to live... as does everyone else. For this reason, it is very important to me that I live my life the best that I can and do my best to help others do the same. Doing harm to another is wrong because you a preventing them from enjoying their life, taking from them something that can never be replaced. To an atheist doing the right thing is far more important than it is to a theist, after all... in the grand scheme of things does it really matter if you are murdered if you end up in heaven? Atheists are some of the most moral people around, we have to live with the consequences of our actions. Finally, an atheist doesn't need to be punished or rewarded to know right from wrong... in the end, who is the moral one?
This was a few years ago, but she pretty much refused to admit that I could possibly be moral and we moved on to talking about the impossible nature of two people populating the entire world. One would think that someone interested in science and competing in biology events would realize that two people cannot possibly create a stable population. Oh, and she said something about Adam and several of his offspring living 10,000 years (this is where I stopped listening) and thats how they had enough kids to do it... still doesn't solve the inbreeding problem though does it?
Jeremy...there are so many other Biblical facts that you can attack for their absurdity.
Noah's Ark? All animals are within walking distance of one guy's boat that has no climate control??
Jacob wrestling an angel and beating a blessing out of him?
What about the fact that the Bible is no moral compass for ANYONE at all. Look at the rape that is approved or ordered by god (there is a thread on this site that might really help you with direct passages) and misogyny, domestic violence and child abuse/murder. I wouldn't trust anyone that took the 'word of god' as literal. That's how folks like Andrea Yates are raised. Hell, she would have been celebrated a few centuries ago.
It is often pretty easy to remind Christians that their morality is not really coming from the bible, if you can prevent them from going on the defensive about it.
Just pull out one of the many morally despicable quotes from the bible (eg: stoning children to death for talking back to their parents) and ask the Christian if they would do the same thing in that situation because it was the right thing to do. They'll have some excuse why they wouldn't do the same thing themselves, because they have a way to make moral choices outside of following the bible.
Usually, there are also lots of example you could use from real life. Most Catholics I know fully endorse the use of contraception, don't actually believe that crackers and wine turn into flesh and blood, don't believe the pope is really perfect and infallible, and do support gay marriage rights. Just for example. They are making moral choices outside of the teachings of their religions.
At this point it becomes obvious that atheists can do the same.