Hi Mike - What a great picture!!! (and great scan, except for the dust)
Obviously, the best way to fix this is to re-scan the photo after cleaning it carefully.
However, even if you do that, there will always be some remnant (white) dust and dark spots, so here's how to treat this problem in a semi-automatic way using the Dust and Scratches filter.
Make two copies of the original. Set the blend mode of one to darken (this will take care of the white spots), and set the other to "lighten" (to take care of the dark spots).
Apply the D&S filter to each layer, in turn. Adjust the sliders in the D&S dialog boxes for the best removal without mucking up the surroundings too badly.
Make a new layer on top (cntl-alt-shift-E) that combines the effect of both D&S layers.
Temporarily, mask it completely black and turn off the individual D&S layers below it.
Even at their best, these filters always produce significant artifacts around desirable bright spots/edges, as well as desirable dark spots and edges, so the idea is to roughly brush in white into the mask in areas where the dust is most objectionable, but leave important areas (the face, the chrome of the bike, etc.) masked in black.
The following screen grabs should be self-explanatory.
HTH,
T
Attachment: first, the layer stack
