You know those images that are entirely in black-and-white, save for some part like a woman's lips, which are in colour? This tutorial will teach you how to achieve that effect. (This tutorial was designed and tested in Photoshop CS2/CS, but it should work in earlier versions and in PSP.)

1. Duplicate the layer with the image you want to work with.

Layer -> Duplicate Layer, or right-click on the layer and select "Duplicate Layer".

2. Desaturate (make black-and-white) the duplicated layer, NOT the original layer.

Image -> Adjustments -> Desaturate.

3. Making sure the second (desaturated) layer is selected, cut out the parts you want to be in colour.

Technically, that's the end, but most likely, your image will look kind of flat. To remedy that, you can play around with the Curves (Image -> Adjustments -> Curves) or the Brightness/Contrast sliders (Image -> Adjustments -> Brightness/Contrast) on the desaturated layer, and you can use pretty much any of the settings in the Image -> Adjustments menu on the colour layer.

Have fun! If you have any questions, you can PM me. Oh, and if you found this tutorial useful, I would be very grateful if you clicked the scales in the upper-right-hand corner of this post. ;)