Minimiser toutes les fenêtres

procedure TForm1.Button1Click(Sender: TObject);
var
h:HWnd;

begin
h:=handle;
while h > 0 do
begin
if isWindowVisible(h) then
postmessage(h,WM_SYSCOMMAND,SC_MINIMIZE,0);
h:=getnextwindow(h,GW_HWNDNEXT);
end;
end;