mod_python embeds the python interpreter into the apache server. This saves initialization time and the need of forking cgi scripts. It doesn't have the ability to run as different users. It will always run as the main apache user and group. Be sure that your wiki data files are accessible and writable by your apache server.
The basic configuration is suitable for mod_python 3.1.3 and later. If you use older version, see the section "Older mod_python versions"
mod_python will cause your apache processes to increase their memory requirements considerably - especially as apache runs many separate processes which will each need to have their own copy of the python code and data in the process memory space. You may find that FastCGI, as detailed in HelpOnInstalling/FastCgi is rather more efficient in this respect.