The most common problem you might encounter is when you have an old Python version installed into "/usr", and a newer Python distribution into "/usr/local"; this is typical for GNU/Linux distributions that still come bundled with an old Python version.
In that case, if you enter "python" on your prompt, you will usually get the more recent Python interpreter, because "/usr/local/bin" is in your PATH. The situation is different in your webserver environment, and thus you might have to change the bang path of "moin.cgi", like this:
""" MoinMoin - CGI Driver Script ... """
When installing, make sure you install with the version of python you want to run moin with. python setup.py install will install with the first python in the path, which may be the version you expect or not! /usr/local/bin/python2.4 will install in specific python. You will have to use the same path in the moin server script.