The December 2003 issue of Photoshop User Magazine demonstrated what appears to be a pretty simple way of doing this. I have never tried it, but here are the steps if you want to try. Post a before and after when you are done and let us know if this really works:
1. Open your image
2. Duplicate the Background Layer
3. Go under Image --> Adjustments and choose Selective Color
4. When the dialog comes up, change the colors pick list to "Red" and enter 0 for Cyan, +70 for Megenta, +100 for Yellow and +84 for Black and make sure Relative is checked. Don't press OK
5. In the same Selective Color diaglog, change the colors pick list to "Whites" and enter 0 for Cyan, +67 for Magenta, +97 for Yellow, +51 for Black and make sure Relative is checked. Press OK.
6. Choose the History Brush from the tool box, go to the History palette and click in the left column next to the words Duplicate Layer.
7. Choose a fairly large, soft-edged Brush and paint back the areas you don't want to become tan (hair, shirt, etc.)
8. If the effect is too strong (too tan), lower the opacity for this duplicate layer.