lots of point and shoot cams have a selective color setting. i don't think any dslr's do. its much easier to do in photoshop. It is a bad thing to do it in camera, because then it will forever be a selective color image....
I don't know how experienced you are with photoshop, so here is a super elementary way of doing this...
http://video.google.com/videoplay?do...3426593215811#
of course it would be better to use layer masks and adjustment layers, but its more complex.