Mottled render using ambient occlusion

I’m new to Blender, and am learning the ropes by working through “The Essential Blender” book. Chapter 4 (Mesh Modeling) has the user “light” a scene with ambient occlusion. Unfortunately, the resulting render on my computer is mottled with black spots over detailed areas of geometry:

This is a render of the same model (though a little later in the project) without ambient occlusion, lit with a standard lamp:

I believe the problem is the integrated Intel G45/G43 Express Chipset my computer uses, instead of a standalone GPU. Could anyone confirm this, or tell me how to correct it? Using Blender version 2.49, running Windows 7, lots of ram and a powerful processor. I’ve also tampered with the mesh’s normals to no avail.

Thank you!

It looks like a problem with overlapping faces, have you tried selecting all vertices (a) and doing w > remove doubles?

You have overlapping meshes. Someone else had exactly the same problem with the same model. If you have a mirror modifier check you have applied it correctly as this caused his problem, nothing to do with the graphics card.

Thanks for the quick response! That eliminated the problem immediately.