Ler XLS pra StringGrid

uses comobj;

var
  Excel: Variant;
  Linha, CN: Integer;
  arq : TFileName;
begin
  Excel := CreateOleObject('Excel.Application');
  Excel.Visible := false;
  OpenDialog1.Execute;
  arq := OpenDialog1.FileName;
  Excel.WorkBooks.Open(arq);

  Linha:=3;

  StringGrid1.RowCount := 1;
  StringGrid1.ColCount := 4;
  StringGrid1.Cells[1,0] := 'BOLETO';
  StringGrid1.Cells[2,0] := 'VALOR';

  CN := 1 ;

  While Linha < 1000 Do
  begin
    StringGrid1.RowCount := CN;
    StringGrid1.Cells[0,CN] := IntToStr(CN);
    StringGrid1.Cells[1,CN] := Excel.WorkBooks[1].Sheets[1].Cells[LINHA,1];
    StringGrid1.Cells[2,CN] := Excel.WorkBooks[1].Sheets[1].Cells[LINHA,3];

    IF Length(StringGrid1.Cells[1,CN]) = 0 THEN
    begin
      Excel.quit ;
      EXIT ;
    end ;

    CN := CN + 1 ;
    linha := linha + 2 ;
  end;

 end;