Welcome to Forums, Dave!
Don't have any samples handy so here is just a logic:
Since MDI forms don't respond to Key events (Down, Up, Press) you'll have to subclass either VK_DOWN/UP or WM_KEYDOWN/UP (whichever works better) messages utilizing GetAsyncKeyState() api function. I'm sure searching forum or googling will give you some samples.
Here are the declarations:
VB Code:
Option Explicit
Private Const VK_DOWN = &H28
Private Const VK_UP = &H26
Private Const WM_KEYDOWN = &H100
Private Const WM_KEYUP = &H101
Private Declare Function GetAsyncKeyState Lib "user32" _
(ByVal vKey As Long) As Integer