In this video tutorial I try to show how to create ambient occlusion in 3ds max. I use max 9. First change render setting to mental ray then apply mental ray shader to all object this can be done by material override setting in render setting. In mental ray shader apply ambient occlusion texture and adjust its value to get final output, remember to change background color also.

To understand how ambient occlusion work visit this page http://en.wikipedia.org/wiki/Ambient_occlusion

High res video is here