Making color photo partly B&W

I cannot figure out how to make a photo all black and white except for a part of it, like a rose. Can someone either tell me how to do this, or point me to a website or tutorial that could show me how? Thanks and happy PSing :D

you would have to select the rose, either by the pen tool or lasso, and inverse the selection. Then just desaturate the selected area (CTRL+SHIFT+U I believe).

or if you wanted the rose to be a different color you could desaturate the entire thing then select the rose and play around with its color balance