Shoutbox

Fn key is a pain in the posterior.  There is no standard and different vendors implement it differently.

In some cases, Fn key itself will have a keycode and when pressed in combination with certain other keys, cause them to produce different keycodes.  In other cases, it may not have a keycode of its own, but the combinations still do.  In yet other implementations, Fn key combinations trigger ACPI events and thus have no keycodes at all. 

It sounds like that may be the case with yours.  It is possible to programmatically hook (or trigger) ACPI events, but keyboard mapping software wouldn't be of much help there.

Although you are using Windows, this is a hardware question and you should be a able to Google up a lot of discussion of this (possibly including information specific to your laptop brand and model) in the context of running Linux on laptops.  Linux laptop user community has invested a lot of time trying to make use of the the Fn key combinations and discovering how different vendor implementations work.