Here is how to set up MediaWiki on a subdomain and use pretty/short URLs. This was tested on July 1, 2010 with MediaWiki 1.15.4, PHP 5.2.8, MySQL 5.0.90 and Apache 2.2.11.

This assumes you are in a shared hosting situation, and do not have root access and cannot edit the Apache configuration files directly.

Your setup

Suppose you have a site, www.ilikefish.com. Its DocumentRoot is /var/www/ilikefish.com. You then create a subdomain, wiki.ilikefish.com, with a DocumentRoot of /var/www/ilikefish.com/wiki.

Configuring Apache

1. In /var/www/ilikefish.com/.htaccess, set up a redirect
   

   RedirectMatch /wiki/(.*) http://wiki.ilikefish.com/$1

2. In /var/www/ilikefish.com/wiki/.htaccess, set up rewrite rules:
   

   RewriteEngine On
   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule . /index.php [L]

Configuring MediaWiki

1. In LocalSettings.php, set the following variables:
   

   $wgScriptPath = "";
   $wgArticlePath = "/$1";
   $wgUsePathInfo = true;
   $wgLogo = "/my_fish_logo.png";
   $wgScriptExtension = ".php";