Ok, here's my really quick explanation of how to use ID maps to blend between different materials on an object. You would create each different material (I've only done 2 so far on an object, I'm sure you could do it for more though), so say a lambert and a blinn, and attach the colour map to each one. Then, you would use an ID map to specify where you want the lambert material to show through, and where you want the blinn. You use a blend utility node to blend between the 2 materials, using the ID map as the blender, and then plug the result into a layered shader, which you apply to your object.