On a lab machine where I can't just go clobbering things, there appears to be more than one version of python installed.  
If I python --version I see 2.7.1.   
I've installed numpy via "apt-get install numpy" and it says it is installed, but when I try to import it it isn't found.  
When I do a find on the machine for numpy I see it in the /usr/lib/python2.5/site-packages/numpy folder.  I assume this is the problem... that apt-get put it in the 2.5 version instead of the 2.7.  
How do I resolve this?  Is there a way to tell apt-get which python I'm talking about when I do an install?  Or do I abandon aptitude and use pip or something?
Apt/dpkg have a Debian way of managing multiple installed versions of Python (I believe it is called python-support).  Any extra package, like numpy, that you install will automatically be built and available for all the versions of Python supported by that package AND installed by dpkg.  Since numpy supports every Python, your info tells me that the only Debian python package on your system is 2.5, and the 2.7 in your PATH is probably in /usr/local.  When you install the numpy package it doesn't know about the locally built 2.7.   You can always easy_install. 
The suggestion to use virtualenv is a good one. I have a production system I support using python 2.5, which has been dropped from debian unstable; virtualenv makes it possible to work with whatever version you need.  SInce python is needed by so many tools it's better leave system python at whatever Debian wants it to be.
Multiple versions of python when installing a package with aptitude