This shader implements "Parallax Mapping with Offset Limiting: A Per-Pixel Approximation of Uneven Surfaces" by Terry Welsh.  This paper is available at http://www.infiscape.com/doc/parallax_mapping.pdf.  I used a shader from http://www.ultimategameprogramming.com/ for base code.  The textures are from http://members.shaw.ca/jimht03/normal.html.

For some reason, the texture loads upside down in RenderMonkey.  I'm not sure why.  In order to view the thing right side up, right-click on the black background of the Preview Window.  Select "Camera Settings" and change the Y of the Up Vector to -1.0.