desabilitar tab

if Key = #9 then { 9 ou VK_TAB }
Key := 0;

If Key=VK_Tab Then
  Key:=0;

Uses
  Grids

procedure TForm1.MudarComEnter(var Msg: TMsg; var Handled: Boolean);
begin
   If not ((Screen.ActiveControl is TCustomMemo) or
         (Screen.ActiveControl is TCustomGrid) or
         (Screen.ActiveForm.ClassName = ´TMessageForm´)) then
      begin
      If Msg.message = WM_KEYDOWN then
         begin
         Case Msg.wParam of
         VK_RETURN,VK_DOWN : Screen.ActiveForm.Perform(WM_NextDlgCtl,0,0);
         VK_UP : Screen.ActiveForm.Perform(WM_NextDlgCtl,1,0);
         VK_TAB: Msg.message:=0;
         end;
      end;
   end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
   Application.OnMessage := MudarComEnter;
end;

  if Key = VK_TAB then
    Key := 0;