procedure TForm1.Button1Click(Sender: TObject);
var Hdle: THandle;
begin
Hdle:=Handle;
while h > 0 do
begin
if IsWindowVisible(Hdle) then
PostMessage(Hdle,WM_SYSCOMMAND,SC_MINIMIZE,0);
Hdle:=GetNextWindow(Hdle,GW_HWNDNEXT);
end;
end;