you open the texture mpa file in photoshop. you then follow PhilC's procedure - by creating a new layer "above" the texture, and on that new layer. You create your bump map "above", using the texture map layer "below" as a template. When completed, you then make sure the bump map layer completely covers the texture layer (you can do that by selecting all in the bump map layer, and filling the whole layer with white in the multiply mode), then flatten the image, then save it with a different name - or you won't have a texture map anymore!