The main thing is to make sure that you have GlovePIE configured correctly.
This is the GlovePIE script that I use, modified from "Honkey Kong"s from the fretsonfire forums.
Code:
// Note: This commented-out block is what I used to test each button
// while I figured out how the guitar worked.
z = Wiimote.Classic.a
x = Wiimote.Classic.b
c = Wiimote.Classic.x
v = Wiimote.Classic.y
b = Wiimote.Classic.ZL
RightShift = Wiimote.Classic.Up
RightControl = Wiimote.Classic.Down
// Press the Right Alt button (Whammy) when the whammy bar is depressed
// To tweak the timing of how far down you need to tilt the whammy
// bar to hit the key, alter the value to the left of < Wiimote
// For Referance, my whammy ranges from 0.52 at rest to 0.84 fully pressed
// whammy
Key.RightAlt = (0.6 < Wiimote.Classic.R < 0.84)
//Star Power
Key.Space = (20 < Wiimote.RawForceZ < 100)
Wiimote.LED1 = 9
Key.Space = Wiimote.Classic.Minus //Star Power
Key.Escape = Wiimote.Classic.Plus //Menu / Pause
Key.Left = (-1.2 < Wiimote.Classic.Joy1X < -0.5) // Joystick moving Left = minus X axis
Key.Right = (0.5 < Wiimote.Classic.Joy1X < 1.2) // Joystick moving Right = positive X axis
Key.Up = (-1.2 < Wiimote.Classic.Joy1Y < -0.5) // Joystick moving Up = negative Y axis
Key.Down = (0.5 < Wiimote.Classic.Joy1Y < 1.2) // Joystick moving Down = positive Y axis
You can test that its working by opening up notepad, and checking if numbers/letter appear as you press buttons on the guitar. You then need to setup the keyboard mapping in FoF to match your buttons (since all GlovePIE does is maps wiimote buttons/motions to a keyboard press)