generally, if you can't tell the difference between two models, choose the cheaper one.
the reasoning is that you only need the more expensive one when there are features in it that you really need to use.
of course, most beginners won't know which is better, in which case, getting ANY of the cameras makes no diff to you.
so being specific, get the d50. when u finally realise that you've used the crap out of the d50 and need to upgrade, there won't be a d70 to think about anymore, it'll be the next "grade" up.
of course, the d70s (d70 has been replaced) is a better camera, but for a beginner it probably won't make a difference. besides, the d70s is soon to be replaced by (probably) a d80.
i wouldn't worry too much about the body. once u get either, u will start worrying about lenses, that one even more headache.
good luck and buy already PLEASE shoot with it.. if u let it collect dust, let me know your address.