You can also use a composite map in the diffuse slot to mix a bunch of different maps. In a standard material, in the diffuse slot instead of putting your bitmap (.tga, .png, .jpg ect...) but a composite map. Then create new layers, loading your bitmaps into the left slot, and masks into the right slot. You can set the…
You can't apply multiple material IDs to a single face. What you want to do is using a more complex material - for example, use a "Mix" map in the diffuse slot, use your "base" texture at the lower level, and your "on top" texture (eg. the sleeve or the glove) at the higher level. Then use the mask image for that "on top"…