as suggested elsewhere, macports works fine on multiple architecture and versions of MacOsX + allows updates and more:
$ port search numpy
py-numpy @1.3.0 (python)
The core utilities for the scientific library scipy for Python
py25-numpy @1.3.0 (python)
The core utilities for the scientific library scipy for Python
py25-symeig @1.4 (python, science)
Symeig - Symmetrical eigenvalue routines for NumPy.
py26-numpy @1.3.0 (python)
The core utilities for the scientific library scipy for Python
py26-scikits-audiolab @0.10.2 (python, science, audio)
Audiolab is a python toolbox to read/write audio files from numpy arrays
Found 5 ports.
$
in your case, simply issue :
$ sudo port install py26-numpy
alternatively, if you want / need to compile yourself, the instructions in HJBlog are very useful. I tested and could easily compile the 64-bit version of matplotlib.