Try looking at the configuration file for httpd.  It's someplace like /etc/httpd/conf/httpd.conf  I am by no means an expert at html/cgi (although I'm trying to learn!), but I know that httpd.conf is where things like Apache pathname configuration are handled.  Basically, you can define which directory will be the starting point for a given URL pointing to your server.  Note that the starting point may differ depending on whether you're executing a script (CGI) or simply fetching a file.  So if you have /public_html configured as the "starting point", an URL which references your server will access files relative to the /public_html directory.

You may also want to read some of the Apache/http documention (try a Google for "configuring html", or something similar).  Good luck!