Also Paolo's recommendation of looking at a brush-based displacement type program is a good one.

You also may want to look into ZBrush as well, it is another similar one.

Those programs allow you to kind of "paint" displacements on top of an existing mesh, you kind of paint brush strokes like you are in Photoshop but those brush strokes create ridges or valleys along the surface.

You should also be able to use different bitmaps as a pattern brush that you can use to stamp a previously drawn 2D design as a relief.

- Michael