The way to eliminate reflections from transparent areas in Poser 5 is to connect the transmap image to the Specular Color input. You can sometimes get problems with JPEGs for transmaps, where higher compression levels give slight colour shifts along edges. Poser 5 will handle a PNG file, which for a transmap can be reduced to just two colours, or one bit, and give a very small file without losing detail. If you want to make the transparent parts reflective, there are ways to invert the black/white with a math node.