I'm pretty sure its just the default P-51D Normal map. I was experimenting with the interplay between the Specular and Environmental map settings and the base colors chosen for the natural metal look, so wasn't concerned with Normal map effects yet.
I think what you're talking about here is the shadow and glare layers along the screw lines that fasten the wing fillet to the fuselage. Basically, for each screw head, create dark spots for shadow up-sun (1 px up, 1 px to toward the front from the screw head) and a light splotch for glare down sun (1px back, 1 px down). Then you adjust the opacity of these layers til you get a believable look that makes the metal look depressed where the screw fastens the sheet metal to the frame underneath. The rivets on the fuselage underneath the canopy also have a faint dark shadow in front of the rivets, and a slight glare line behind (for the vertical rivets).
There is still a lot I have to learn about the Normal maps - I think we are supposed to be able to reproduce this effect using the Normal map instead of shadow & glare layers in the diffuse map (the base skin file). The game's graphic engine should handle creating the proper shadow and glare effect on its own, and adjust it per your viewing angle and the angle of the light source. So far though I've only been focused on trying to get the bare metal look right.
btw, for pxdig, there have been some helpful tutorials written. A couple of old ones are saved here:
http://tjlaven.brinkster.net/ah/These are both old and in need of updates, but still contain helpful info. Greebo also wrote one which I think is stickied at the top of this forum.
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