procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
const
  KeepPrevControl:TWinControl=nil;
var
  i:Integer;
  c:TWinControl;
begin
  if key=vk_down then
  begin
    perform(WM_NEXTDLGCTL,0,0);
    KeepPrevControl:=ActiveControl;
  end;
  if key=vk_up then
  begin
    for i:=0 to ComponentCount-1 do
    begin
      if Components[i] is KeepPrevControl.ClassType then
      begin
        c:=(Components[i] as TWinControl);
        if (c.TabOrder=(KeepPrevControl.TabOrder)-1) then
            ActiveControl:=(Components[i] as TWinControl);
      end;
    end;
  end;
end;