There's a part in the help file which may be useful to anyone reading this, it's the constants used by the input module. Basically it's just which keys you are allowed to use for inputs.
DOWN LEFT RIGHT UP
Numbers corresponding to the directions down, left, right, and up.
A B C X Y Z L R
Numbers corresponding to the various controller buttons.
SHIFT CTRL ALT
Numbers directly corresponding to the keyboard's SHIFT, CTRL, and ALT keys.
F5 F6 F7 F8 F9
Numbers corresponding to the keyboard's function keys. The other function keys are reserved by the system and cannot be obtained.
I'd also like to note that the letters aren't the keys on the keyboard, just the keyboard letters you have assigned to them (You can press f1 while playing to check them out).
If you want to use any key on the keyboard you will probably need to use a keyboard module script, and there is plenty of those around.