when you want to polypainting you must first made uv map and next poly painting with Zbrush 3.1 to 3d head model.
this is about made uv map with program modo.
don't worry very much easy!!!!!
picture1)first open 3d head wave front object file as modo>file>open click.
picture2)next cilck model that's above at interface modo and than 3d model showing modo interface.
picture3)click right makes 3d model showing right side at interface