procedure TForm1.FormCreate(Sender: TObject);
var
  i, intWidth, intMaxWidth: Integer;
begin
  intMaxWidth := 0;
  for i := 0 to ListBox1.Items.Count-1 do
  begin
    intWidth := ListBox1.Canvas.TextWidth
       (ListBox1.Items.Strings[i] + 'x');
    if intMaxWidth < intWidth then
      intMaxWidth := intWidth;
  end;
  SendMessage(ListBox1.Handle, LB_SETHORIZONTALEXTENT,
    intMaxWidth, 0);
end;