I am building Matplotlib on my Mac with Python 2.5 Release Candidate 1.
We use this for our astronomical data-reduction software.
I saw your post on matplotlib-devel and I think I can help a bit. Here are some patches that get it to compile:
patch-_image.cpp (449 Bytes)
patch-agg.cxx (1.08 KB)
patch-cxx_extensions.cxx (4.3 KB)
patch-swig_runtime.h (533 Bytes)