I installed pbrt on my Intel-based MacBook Pro running Mac OS X 10.4. The build and installation instructions were straightforward, especially after installing OpenEXR using Fink. However, I ran into some issues when building the pbrt tools. I ended up having to further modify the Makefile under the tools directory to work around unrecognized flags passed to the linker.
In order to speed up the rendering process, I lowered the resolution to 200 x 200 pixels, used 1 sample per pixel, and 1-2 area samples for test images. Rendering time was relatively fast for the first three configurations. For the fourth configuration, I rendered each light source separately until they looked right individually before rendering the final image with all four lights.
I found it easiest to start with placing the light source in the general position it was supposed to end up, and then incrementally tweaking one parameter at a time to see how it would affect the scene. Whenever I got ahead of myself and changed several parameters at a time, it would take a bit to sort out which changes were satisfactory and which ones were getting me further from what I wanted.
I was initially confused by the main light in the fourth configuration, and spent a long time trying to tweak the parameters of a spot light to get the correct lighting and shadowing on the model. Once I started using an area light, I got much more satisfactory results with the softer shadowing.
What I found helpful throughout the assignment was placing the camera at different points around the scene. This helped me get a better perspective on the positioning of the light sources as well as understanding the effects of geometric transformations. I also experimented a bit with tweaking the color and size of different lights to see the effect on the model.