I've worked out the excellent tutorial on toon shading at: Fenriz.org
I'm presently working on a PSA for television. Here is an example of my Mental Ray toon shaded character: 
The reason I'm here is mental ray slams the door in my face when I attempt to add a UV mapped lambert shader to my girl's dress front. My idea was to combine the toon shader as one layer and the mapped UV star in the second. Here is an example of the star rendered in the Maya Renderer: 
When I attempt to render in Mental Ray the display window simply pulls up the last image rendered and ends there.
Where have I gone wrong?