Shara - you certainly know your way around Photoshop.
d_jay - one other thing I'd like to add is a comment about the termination of the hair; nailing it goes a long way toward selling the head-transplant. The easiest way to quickly do this in a pic like yours, where the hair colors aren't too far apart, would be to start blending Kim's hair into the model's hair with the erase tool a bit higher up; the other option is lots of careful selection and masking.