[mod_python] PYTHONPATH question

I'm new to [mod_]python and I'm having trouble with PYTHONPATH.  
When I import MySQLdb using the interactive command line,it works fine.  When I import MySQLdb into a module called by mod_python, I get this: 

ImportError: No module named MySQLdb

I've tried setting the PYTHONPATH environment var in httpd.conf using the Apache directive SetEnv, but still no good.

What am I missing?  Does mod_python run python modules as the Apache user?  If so, what's the best way to set the value of PYTHONPATH?

 - thanks in advance,
 - andy