Here is my quick attempt at replacing the sky in Jenny's photo at http://pg.photos.yahoo.com/ph/jazzmin1962/detail?.dir=/9b32&.dnm=b5ba.jpg&.src=ph
First, I found a photo I had of some sky and placed it in a layer under Jenny's photo.
Then I darkened Jenny's photo with levels, then used the Magic Wand at 80% to select the sky. Pressed the Delete key and bingo! My sky popped up.
Tom M. (MrQuietGuy)