how does one set the plpython python interpreter?

Hello,
Hopefully this hasn't been answered already. I attempted to do full
due-diligence on it, and could find no answer anywhere.

Basically my problem is that my server has both python 2.3 and python
2.4 installed (strange but unavoidable reasons behind this), and it
appears that my installation of postgres is using the 2.3 version for
my plpython scripts - and I need it to use the python 2.4 version.

The 2.4 version is first in all the paths including user postgres on
my server, but it seems to keep using python 2.3.

Where can I configure which version (or path) that postgres will use?
I assume that a python interpreter is not included inside the
postgresql-python addon, and that it just uses an already-installed
python interpreter.

As a corollary, if I can configure the path to the python interpreter
then I should be able to install my own python libraries for plpython
to use (and since it's "untrusted" anyways...), correct?

Many thanks if anyone can shed some light on this.
-Roger