Clean URLs in Mac OS X Server
For Mac OS X Server 10.4 (Tiger Server) and most likely previous versions as well, do not make changes to /etc/httpd/httpd.conf expecting the AllowOverride All directive to work. The correct file to add the AllowOverride All directive is in the directory /etc/httpd/sites/. In that directory are the virtual host configuration files. Each virtual server has a configuration file in that directory so it is in those files that you must enable AllowOverride All. If you only have one web server on your server configured, then the file you want to modify is /etc/httpd/sites/0000_any_80_.conf.
Client & Server
This page shouldn't be marked "Server" as these instructions are generic to both the Client and Server versions of OSX.
Your Apache conf is at /private/etc/httpd/httpd.conf
You can stop/start the web server using the Sharing > Personal Web Sharing preferences pane.
Change AllowOverrides in yourname.conf
I'm running 10.5 (not server) and I had to go to /private/etc/apache2/users/myname.conf and change AllowOverrides to All, because I made my web root /Users/myname/Sites in the main httpd.conf file.
Doug Gough
ImageX Media