var Workbook: IXLSWorkbook;
begin
  Workbook := TXLSWorkbook.Create;
  Workbook.Sheets.Add;
  Workbook.Sheets[1].Name := 'Sheet1';
  {...}
  Workbook.SaveAs('C:\book.xls');
  Workbook.SaveAsHTML('C:\book.html');
  Workbook.SaveAsRTF('C:\book.rtf');
end;