final gather is what you're after.....

Here's some instructions to get the most basic of final gather renders.

1: make a ground plane (larger than the scene)

2: apply a lambert shader to it with the R,G abd B values set to 1.25

3: open up the outliner and double click the persp camera (or whatever camera you're using to render) and set it's environment slider to white.

4: open up the render globals and set the renderer to mentalray. under the common tab, turn off the Enable Default Light switch and then under the mentalray tab select preview final gather.

Hit the render button and this is the effect you get......

(obviously if you play with the render settings you will get better quality images, all I have given here is a nudge in the right direction).