How do I make one object in color in a black and white photo-Photoshop elements 10?

There are actually a lot of ways to do this - with two copies and the eraser tool, with two copies and a mask - but we're lucky because, since Elements version 7, we've had a Smart Brush and a very easy way to do this very quickly. The video tells (and shows) how. (Yes, it's for Elements 7 but everything looks and works the same way in versions 8, 9 and 10;-)

http://www.alibony.com/video/video-lesson15.htm

If you are beginning with a color-photograph, make two copies of the photo on separate layers: the lower layer will be the colored one and the top layer will be the black and white photo. Simply erase the portion of the B&W image (use the Magic Wand, eraser, pen, whatever you wish), and you will have the color shining through the black and white.

I dont use elements, but i assume youd just make a black and white mask and erase the parts you want in colour