If you have Excel 2007, you can save the file in a variety of
formats, and one of them is the format for Excel 97 - 2003 which is probably
most common.  I found these online. Add these values to excel.ch:
50 = xlExcel12 (Excel Binary Workbook in 2007 with or without macro's, xlsb)
51 = xlOpenXMLWorkbook (without macro's in 2007, xlsx)
52 = xlOpenXMLWorkbookMacroEnabled (with or without macro's in 2007, xlsm)
56 = xlExcel8 (97-2003 format in Excel 2007, xls)