How to turn off Function Keys permanently

You can only disable F8-F12 and F14,15 which you already have done but I don't think Leopard uses the other F-keys for anything. At the bottom of Keyboard shortcuts you can assign an application's menu commands to a user defined key.

Before you go to the trouble of entering all the keys see if the Quark default F-Keys will work. I don't have much in the way of apps loaded on Leopard yet but the default Photoshop F-keys work without my disabling anything in keyboard shortcuts. F9 still brings up Expose in Photoshop but I haven't disabled it. I don't know, however, if Quark XPress works that way, though. They tend to play by their own rules

In System Preferences > Keyboard and Mouse go to the Keyboard Shortcuts tab. Scroll down to see the function keys. Unchecking should disable the function keys.