On my iBook G4, I've got it set so you have to hit Fn to get the secondary function of an F-key. So, brightness is normally Fn-F1 and Fn-F2. Volume is Fn-F3 through F5.
On my external keyboard, in the default configuration (with the thing requiring hitting Fn to get the secondary function set, but that shouldn't apply to an external keyboard, and of course, before I got that program) the keys work as normal F-keys, with the exception of F12 (which when HELD acts as the same as Fn-F12 on the internal keyboard - eject,) Scroll Lock (aka F14,) which by default has the same function as Fn-F1, and Pause (aka F15,) which by default has the same function as Fn-F2.
And, I'm using Print Screen, Scroll Lock, and Pause because they're three essentially useless keys on a Mac, and my external keyboard has those keys.
When I disabled those shortcuts, it did
NOT disable the internal shortcuts on the iBook, only on the external board. As my Mac doesn't have F13 through F15 internally, it makes no difference to the internal functions.