Here's an easy way to achieve these results:

Color:


Ambient occlusion:


Mix (Color + Ambient Occlusion)


Create two surface shaders. Connect an mib_amb_occlusion node to the default of one of the surface shaders. This will be your ambient occlusion shader. Now, take your normal shader, the one you want to apply the occlusion on to. Display these two in your hypershade's work area. Create a multiply divide node. Attach the normal shader's out color, to input1, and the occlusion shader's out color to input2. Connect the output of this node to the default of the second surface shader you created. Assign this surface shader to your model.

The first shader (your normal) will take care of all shading information. Lighting, transparency, etc. The occlusion is just multiplied onto the normal material, much like it would be done in a compositing application.

Hope this helps.