easiest way (also good results)
dark layer with blocked shadows on the bottom
light layer with blown highlights on the top
top layer active then simultaneously press ctrl alt ~
Once you see what's going on, you can get fancier by saving the selection as a mask etc. etc. etc.
Or learn this technique: [a href=\"http://www.luminous-landscape.com/tutorials/digital-blending.shtml]http://www.luminous-landscape.com/tutorial...-blending.shtml[/url]