I don't read the help files as much as I should, but I still think they are pretty good.
I'm at work so I can't post any pictures, but that shouldn't be a problem.
Ok, first open up your hypershade and create a new lambert material - windows>rendering editors>hypershade. Now select all of your objects in your scene, back click on the lambert and pick assign material to selection. Now back click on your model, scroll down to materials and pick material attributes. there are two tabs at the top. select the one that says lambert_SG. open up the mental ray tab and under custom shaders click the map button next to the material shader. Another window will open up. select the mental ray tab at the top and scroll down to the textures section and pick mib_amb-occlusion. the attribute editor for the mib_amb_occlusion will open up. Try increasing the samples to something like 256. You may also need to increase the max distance, though some people told me that you don't need to touch this, though I couldn't get it to work until I made this number relative to the size of my scene.
Ok, last you need to select mental ray as your renderer. Just open up the render settings window (it's the button to the right of the IPR button at the top) and select mental ray. Now try rendering.
as easy as.... x y z.