I found several hints that mentioned how to modify apache using /etc/httpd/httpd.conf or /etc/httpd/users/user_name.conf, but no mention of how to make changes to Mac OS X Server.
System wide changes can be made in Server Admin or in the httpd.conf file (Apple has even added extra comments relevant to Panther Server telling you what you should and shouldn't touch). However, I quickly found that the information for my site couldn't be found in httpd.conf.
It turns out 10.3 Server has a "sites" folder in /etc/httpd, much like the "users" folder on 10.3 Client, and that every site on your server (even if you only have one) is set up as a virtual host. Within the sites folder will be at least one (probably two or more) .conf files: virtual_host_global.conf, plus a conf file for each site you have set up (named using a serial number plus the port and host name of your site).
As hinted at above, the site's .conf file is simply a <VirtualHost> section that gets included with the main httpd.conf file (the last line of my httpd.conf is Include "/etc/httpd/sites/*.conf"). As such, the contents will be familiar to you if you've used httpd.conf and VirtualHost before (and if you haven't, there are many helpful sites on the web about Apache).
For example, I needed to use ProxyPass to make a non-Apache webserver (zope) running on port 9080 appear to be running at port 80. I created a new site in Server Admin, left all the settings as default, and enabled the site. I then put the following in the conf file it created:
## Default Virtual Host Configuration
<VirtualHost *:16080>
ServerName intranet.example.com
ServerAdmin webmaster@example.com
ProxyPass / http://intranet.example.com:9080/
ProxyPassReverse / http://intranet.example.com:9080/
</VirtualHost>
Observant readers will notice that according to the VirtualHost directives, this site is running at port 16080 rather than port 80 (or whichever port you chose originally). In actual fact, it's available at both. It runs at port 16080, but Mac OS X Server automatically aliases it to port 80 (or whichever port you chose originally).Mac OS X Hints
http://hints.macworld.com/article.php?story=20031216023228773