Try Alpha Masking. Excellent tutorials on alpha masking, by Crazy Man Dan, can be found here and here. You will have to download a plugin for this, but if I understand correctly installing plugins is no longer a problem for you. The way I would do it would be to create a mask of whatever object you want to keep colored, save the mask, go back to your original picture, duplicate the layer, run the Black and White adjustment on the top layer, then run your alpha mask on the top layer. It should come out looking the way you want it.
EDIT: Fixed broken URL tag - sorry about that.