My interfaces to slot systems use the following API's for IPC:
 
    CallWindowProc
    CopyMemory
    GetDesktopWindow
    GetWindow
    GetWindowText
    SendMessage
    SetWindowLong
 
The process is:
 
SetWindowLong to trap windows messages in your message handler.
 
Send a message:
    GetDesktopWindow for the topmost window handle.
    Loop until found
        GetWindowText to see the window caption
        If destination window is found,
            CopyMemory to build a byte array (it's a VB convolution)
            SendMessage to the window
        end if
        GetWindow for next window in chain
   loop
 
To receive messages:
    CopyMemory in your message handler to access the text.  (This may be a VB thing, also)
    CallWindowProc to resume message processing
 
SetWindowLong to unhook your program from windows messages.
 
I hope this is helpful.  If you haven't called API's from VB, it may seem like unnecessary steps are performed.  That's because some C++ datatypes are not present in VB.