OKAY, first thing you have to do it select your model, with the object select. Then you right click, and mouse-over UV something or another, and choose direct. The next step is really learn-as-you-go, but after you figure it out, and have your image, you'll want to go to the outliner window, and right click the UV Map and choose "Make External". Take your pick of an image editor, edit the image you externalized, and when finished, save the image, go back into W3D, and right click the UV Map again in the outliner window, this time choose "Refresh".
Thats pretty much it, all off of memory.
Problems? Yes I used to have those...until I went insane.