Les basically explained it with layer masking, if you understand layer masking you can do anything by copying from any photo a new layer above your background and using a mask to blend them together using the paint brush tool adding white and black to the layer mask itself. In photoshop open the layer's palette and find the "add layer mask" button on the bottom tool bar of the palette. You can see a new layer mask when you see a white square next to your picture or layer selected in the palette. It will be outlined with a heavier line around it, make sure you watch this because it is one clue that your painting on the mask and not the picture. If you haven't tried it already, layer masking is the main key to PS work.
It is easier then you might think.
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