It finally became impossible for me to install Mapnik on a Mac running Snow Leopard. There are just too many conflicts between the Python installed by Snow Leopard and the Python from Macports that Mapnik wants you to install. I suspect it is because both a version 2.6, so if you run:

Bleach:~ mnewman$ sudo python_select python26

How do you ever know which version 2.6 has been selected?

Anyway, I gave up on the Mac and moved to Ubuntu, a linux variant which I run on my Mac using Sun's VirtualBox.

I installed Mapnik using the Synaptic package manager. This took less than half an hour. After fumbling a bit with the "Hello World" tutorial:

http://trac.mapnik.org/wiki/GettingStarted

I was actually able to produce a map:

http://www.mgnewman.com/sz/world.png

I suppose the next step is to try to actually learn Mapnik. It looks daunting.