It may not be as simple as a reversed normal. I recently built a simple model of a picture in a frame in Ligthwave. It was exported as an obj and picked up by UVmapper.

I used UVmapper's "box" mapping to find out that the "picture" insert actually had TWO normals... and that each side of the picture had it's own texture map. Interestingly enough, Poser picks up BOTH sides of the pic and tries to render them too. Results.... interesting to say the least.

Solution. Assign each side of the pic a different material name (e.g., "front" and "back"). Make the "back" material transparent with no colors. voila!

Hope this helps... or maybe all you pros out there already knew this...