How do change a photo to b&w adding color just to a certain object using photoshop?

I know it has to do layers but i'm having difficulty figuring it out!How do change a photo to b%26amp;w adding color just to a certain object using photoshop?
Start with a color image, make a duplicate layer, convert to black and white, then use the eraser to reveal the parts you want in color.How do change a photo to b%26amp;w adding color just to a certain object using photoshop?
Do a quick search in this board--this question comes up daily. :-)
Desaturate, and then use the history brush on the part you want to add the colour (thats the paint brush with a back arrow).



Another way it can be done is by duplicating the image, desturating the top layer, and erasing the part you want in colour. Then the colour image (bottom layer) can obviously be seen where the top layer has been erased.
I'd do a clipping path round what I wanted to keep in colour and make a new layer from this and then desaturate the lower layer. I know you can do it with adjuts levels and select colour and what not but I always find the best result is to take time with your clipping paths and then go from there.