I have a few questions about the Nikon D40 and the Nikon D50... what exactly is the difference?? Does one have a better picture quality then the other? Is the D50 worth the extra $70+? I heard the the D50 has a focusing motor, or something like that... built it, and the D40 does not? is this true? What exactly does the motor do? is it enough to spend the extra $70 for the D50?