function EnumMiniProc(Wnd : HWND; Param : Longint) : Boolean; stdcall;  
begin  
  Result := True;  
  if (Wnd = Param) or (Wnd = Application.Handle) then  
    Exit  
  else if isWindowVisible(Wnd) and not isIconic(Wnd) and isWindow(Wnd) then  
    ShowWindow(Wnd, SW_MINIMIZE);  
end;

EnumWindows(@EnumMiniProc, Handle);