Just my $0.10 on this topic: Stick with the default system Python
2.5.1 on Leopard and save yourself a lot of potential hassle.
In the days of Tiger and its antiquated and hamstrung Python 2.3, many
people were forced to install Python themselves just to get going.
They had to choose between several alternatives: MacPython,
Enthought's EPD, ActiveState Python, etc. This notion of installing
Python on Mac OS X persists to this day, and many people still assume
it is necessary.
If you really want the latest Python or the convenience of a
pre-packaged distribution, go ahead and install one of the fine Mac
Pythons out there. On the other hand, if you just want to get
matplotlib going, the system Python will do just fine. In my
experience it saves you many hassles with CPU architectures during
builds (which has gotten worse under Leopard). I successfully built
and ran the latest MPL r7514 by simply typing "python setup.py build".
No environment variables to be set...
On an aside, Snow Leopard (Mac OS 10.6) looks to have a whole range of
Pythons, from 2.5 all the way up to 3.1. This could make the default
system Python even more of a no-brainer.