If you've installed the Apple Keyboard drivers with AppleKeyboardInstaller.exe (or AppleKeyboardInstaller64.exe) on a PC you'll quickly discover all the function keys are treated as special keys. To get the function keys working normally as you'd expect, it's controlled by a registry key:

[HKEY_CURRENT_USERSoftwareApple Inc.Apple Keyboard Support]

0 = Use function keys 1 = Treat as special keys