You can use maps in the 'lighting' window -- as diffuse colour on the 'object tab', as a background image on the 'back image' tab, or as a lightmap. Note that the diffuse colour choice won't be reflected in the Navi window, but it will show up in the main render. (And you can change it without re-rendering, though like any other change of lighting it will reset the reflections and DOF). The other way to use the maps is in the heightmap formulae like HeightMapIFS -- just put the number in the appropriate parameter slot.
The files have to be in the directory pointed to by the 'background pictures' and 'images for maps' in the initial directory settings, and they have to be file names that are numbers (up to 4 digits, I think.)
I went to town with maps on this one
http://fav.me/d8witd5, but there are much cleverer things that can be done. Some advanced tutorials here:
http://www.fractalforums.com/tutorials/amazing-surface-on-a-heightmap-with-_maptranslate/http://www.fractalforums.com/tutorials/how-to-combinate-2d-and-3d-view-of-an-imagepara-setup/Have fun!