Greetings,
  I was just working through the build/install details for matplotlib on Mac OSX 10.6.8, and building against Python 2.7.1. The reported problem with TK version numbers prevented me from doing "easy_install", and the suggested alternative was to get the latest source (grumble). The recommended command line:

> make -f make.osx PREFIX=<directory> PYVERSION=2.7 fetch deps mpl_install_std

Invokes the building of dependencies, which is fine, except that one of them appears to have a problem:

...
rm -rf libpng-1.5.1 &&\
tar xvfz libpng-1.5.1.tar.gz && \
cd libpng-1.5.1 &&\
./configure  --disable-dependency-tracking  --prefix=/Users/uselton/src/python &&\
make -j3 install
tar: Unrecognized archive format: Inappropriate file type or format
tar: Error exit delayed from previous errors.

A little effort seemed to suggest that the file in question really was not a gzipped tar file. I did not work too hard to discover why that is. I went and got an honest version of libpng-1.5.1.tar.gz and did the "configure;make install", which worked fine. A subsequent invocation of the above matplotlib build line, but without the "deps" also appeared to work. I have since used matplotlib in a simple test and it seemed to work fine. Others who have this problem may be interested that I did get around it. Maintainers may want to take a look with whats up with the automatically downloaded libpng-1.5.1.tar.gz.
Cheers,
Andrew