What I want: http://i.imgur.com/8CDTqVL.png
What I have:
1. I've created the add-on.
2. I've set up an Install.php with SQL containing a table details to store the information.
There's a couple more settings I want to add for this (such as a select where to display the rules, on top of all pages / thread list / only when posting / posting new thread / posting reply ), but if I can just figure out the hooks for the Zend/XenForo classes I can probably handle the rest myself.