The best tutorials on image extraction i've seen to date is by Russell Brown or Dr. Brown as his known and can be found here....
http://av.adobe.com/russellbrown/ExtractSM.mov
Pretty sure this has been upped before either by myself or someone else before the site went down. Honestly what this guy doesn't know about PS isn't worth knowing.
Anyone who hasn't heard or seen any of his tutorials before i would recommend paying a visit to his site here....
http://www.russellbrown.com/tips_tech.html#video