If you want to make something like the right picture, there was a tutorial for doing that in 3dsmax, which was very easy to follow, you just have the different chunks then, but then you could sculpt them. Unfortunately i can´t find it at the moment, but basicaly the chunks were produced proceduraly an then he used a sphere…
I am no sculpter myself, but i do have a tutorial for you by Sascha Henrichs. Worth to take a look at ;) http://area.autodesk.com/tutorials/mudbox_techniques_for_props_2_stone