Jim,
Let me clarify a little (since I've been hammered for this before). What I'm not arguing is that only Christians can be moral. And yes, this whole thing depends on how you define morality. However, my basic argument is that unless humans figure out how to live for ever and transend even the life of the universe we're in, or there is some external judge of our actions, ultimatly all we do has no meaning since nothing we do permenantly effects anything. It then follows to me that if there is no meaning to life and our actions have no ultimate consequence, anything percieved as "good" or "bad" is really only a temproary perception, for in the end all there are are actions without real result. And if there is no "good" or "bad" then there is no morality.

It sounds silly to say, but until we achieve eternal life or unless there's some external being to our existense, even murder isn't really wrong. For ultimately all will be dead, violently or not, and the experiences of our lives will be meaningless. Some have said that the purpose of life is to influence positively those who come after us, but that only works out if someday someone achieves a lasting result with their lives: ie- transends a temporary existense. Otherwise it's "turtles all the way down!"

I've said all of this before and it's been recieved quite negatively, which I understand because it really isn't positive stuff, but it should explain my thoughts on why morality is dependant on there being a God or some impending transendence of humans in the future. I believe if there is a God then morality exists for the Athiest and Christian alike (and since I do believe in God, I also believe in morality), but I also believe that if there is no God, morality cannot exist because there is no real "right" or "wrong" when all is said and done.