There is that nifty lil' app called "DXTBmp" (Google that) capable of opening dds textures and saving them out in some photoshop compatible formats. That is very useful when you want to retexture existing entities. For models you get elsewhere (like turbosquid ore other model resources) you maybe need to make a so called uv map, which you can do with several uv-map programms like ultimate unwrap or lith unwrap. or you get blacksmith paint to paint on your models directly(must be .obj)-but you would have to work on that textures in photoshop to erase the seams....
I am Jacks complete lack of surprise.