I use MSVC 6 so may be some differences.
Simplest method is to insert an accelerator table using the resource builder. Add your ALT+SPACE combo. Call the whole table say, IDA_ACCEL
In your winmain()
Code:
hAccel = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDA_ACCEL));
//error check hAccel
//for both MDI (remove the MDI translate if only a single document app)
while (GetMessage(&msg, (HWND) NULL, 0, 0))
{
if( (!TranslateMDISysAccel( msg.hwnd, &msg)) && (!TranslateAccelerator( msg.hwnd, hAccel, &msg)))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}