Desabilita o botão Fechar do Formulário (topo)

procedure TForm1.FormCreate(Sender: TObject);

var

  hwndHandle : THANDLE;

  hMenuHandle : HMenu;

begin

  hwndHandle := Self.Handle;

  if (hwndHandle <> 0) then

  begin

    hMenuHandle := GetSystemMenu(hwndHandle, FALSE);

    if (hMenuHandle <> 0) then

      DeleteMenu(hMenuHandle, SC_CLOSE, MF_BYCOMMAND);

  end;

end;