There is nothing magic about bumpmapping at all. What bumpmapping does not do, is adding threedimensionality to a model. Its all about enhancing a 2D texture to look more 3D.
The process is quite simple, you need only the normal map plug-in by NVIDIA for Photoshop (i believe there is a similar plug-in for PaintShop too). That is the module you will need also to save a DDS bitmap directly out of Photoshop. You do not even need the Imagetool utility provided in the SDK.

Start with a greyscale image of, i.e. the fuselage. Leave only the parts visible you wish to have bumpmapped. That will be preferably only the rivets, metal plating, screws and things like that. 

Flatten the layers and run it through the normal map filter. Then comes the part not described in the SDK: Go to the channels view, you'll see the three colour channels. If not present, create a alpha. 

Now copy the contents of the red channel into the alpha. 

Make the red channel completely black, invert the green channel and make the blue channel completely white.

Save that bitmap as DXT5 DDS file using the name "SF260_1_T_Bump.dds" (exemple). You have now a bumpmap texture ready for use in FSX.

There is a problem with the SF260 paint kit here: In the kit, you have a "details overlay" layer and that contains not only the rivets but also the dirt and smear. If you bumpmap that layer, you will end up with 3D-looking weathering. So there is much handywork to do.

The other drawback is that bumpmapping can be too strong. Look at the default Cessna or the DC-3: too large looking rivets. The whole thing is overdone. Also, a naked metal skin can look like plastic. You have to play with specular- and bumpmap toghether with alpha, to achieve good results.