Ok if you don't have Focus Magic, here's a way using PS only.

First I duplicated the bg-layer, applied a high pass filter (8.0 px) and set the blending mode to "Soft Light" and opacity to about 40%. Flattened the image.

Then converted to Lab mode for some more sharpening (Lab mode is the ideal mode for sharpening)

Created a new channel from the Lightness channel. Did a "Find Edges" on this new channel and then applied a huge Gaussian Blur to it (5.0 px). Finally added some more contrast. Then used this channel as a selection. (Select -> Load Selection -> Alpha1 then Select -> Invert) and unselected everything in the background. Applied a thorough USM to the lightness channel with the edges selected. Then deselected.

Finally duplicated the bg layer again. Added a mask that included only the people in the front and applied an USM to the lightness channel of this layer.

The result:

http://www.lukaskoning.nl/ret20.jpg

Original:

http://www.pbase.com/image/22988085.jpg


//Focus Magic is an easier solution I guess ;-)