Wait a minute.  If the displacement map is the problem then which Poser version are you using?  I don't believe it was mentioned in the post. 

With any of the Pro series versions, gamma correction is defaulted on in the render settings.  This means that any transparency, bump or displacement maps used in the MAT Room should have their gamma's changed to 1.  Otherwise, the doubling up on gamma settings will definitely cause mesh distortions.