Crayon Effect in Blender 2.5

How can you achieve a cell shaded look that looks like crayons in the compositor? Or is there a simpler way to do this?

smearing soft colored wax on heavy rag paper calls out for multiple layers of textures - look at layering many noise (soft and hard) stucco and other (perlin?) textures to add up so you get that clumpiness and streaking.