Here's how I do it in 2009, hopefully it's the same for 2010.

1. Create a new render layer and add all your objects to it.
2. Right click on the layer and select Attributes
3. Once the attribute editor opens up, you should see a button labeled "Presets" Click on the button and select occlusion.
4. Now render it out.

Just make sure you have Mental Ray selected as the renderer.

To make changes to the occlusion...
1. Window > Render Editor > Hypershade
2. In the hypershade, you should see a solid black surface shader. Double click on it to open it's attributes.
3. In the attribute editor, you should see a tab with ?_amb_occlusion1. Click that tab.
4. Now you can increase the samples (for better render). YOu can adjust the brightness and so forth. Just play around with the options to get a feel for what they do.

Good luck