I think you may be referring to displacement mapping. I’ve gathered these four tutorials for you to illustrate the procedure. There are many others on the Net and many YouTube videos as well. Hope this is what you’re looking for.

http://www.photoshopcafe.com/tutorials/dispmap/dispmap.htm

http://www.heathrowe.com/displacement-map-example/

http://www.photoshopessentials.com/photo-effects/texture-map/

http://psdesignzone.com/displacement-mapping-in-photoshop