Code:

//Find windows that may cover another window.

Var

hW: HWnd;

r: TRect;

begin

hw := Handle;

While IsWindow(hw) Do Begin

   hw := GetWindow( hw, GW_HWNDPREV );

   If IsWindowVisible(hw) and not IsIconic( hw ) Then Begin

     ... use GetWindowRect( hw, r ) to get candidate windows

     rect and check if it intersects the forms BoundsRects via

     IntersectRect

   End;

End;

end;