I am a model who would like to step behind the camera as well and was wondering if anyone could help/teach me how to recreate this type of effect with the color popping off of the blk/wht image

.http://www.modelmayhem.com/pic.php?pic_id=42cc77a8de0df

Selective desaturation is a grossly tedious process if you want to make it look good...and even then it might be for naught.

Haven't checked them out individually, but give these a shot:

Tutorials

Dual layer in PS.
Have a color layer, make a dupe image, turn to grayscale, back to RBG.
Put original color layer over top, but cut out areas you want BW to show...
Selecting areas for cut out can be worked with pentool or splitting contrast...

Come to the Spa shoot today downtown NYC, I will show you...