Hmmm... Ok I am totally useless on photoshop but I can help you with DXTbmp
Right you need DXTbmp to convert the textures into a format that FS
uses to "read" textures DXT3, DXT1 or 32bits.
First after you have finished the repaint in photoshop or paintshop or whatever you use, you open it on DXTbmp simply by drag-and-dropping it into the DXTbmp window. then you add the alpha layer (so that the plane shines in the sim) after that you save it in the format of your preference. on DXT3 the texture will load faster on the aircraft but you compromise a bit of sharpness (not sure if its true), I prefer saving them in 32 bit 888-8 because they look sharper.
Hope this helps.