Update: March 18th, 2010
  1. Download the latest version here.
  2. Goto the admin page of your Joomla! installation and then goto Extensions -> Install/Uninstall.
  3. Under Upload Package File click "Browse" and locate the zip file you downloaded above and then click "Upload File & Install".
  4. Point your browser to and complete the installation procedure.
  5. Go back to your admin panel and goto Extensions -> Plugin Manager.
  6. Locate "System - Wowhead Tooltip BBCode Parser" and enable it.
  7. You're done. The extension will automatically add the armory.js.php, powered.js, armory.css and wowhead.css calls, as well as the call to our whp_parse(); function.

If you're trying to install this script on Joomla! version 1.5 then you should follow the instructions here.