[Dave]

In order to find the right hook which you need, you first check the PHP script the page uses which you want to modify. Then open that PHP file and go to the part where PHP does the logic for that part, you can usually tell by the GET or POST parameters that the page uses.

Then simply look for a hook definition around that location. Note that not every location has a hook so there's a chance you may not be able to do what you want without modifying vBulletin's files itself.