Do you have the Excel application on your computer? If yes, which version do
you have? If you have Excel 97 and the attachment was created in XP or 2003,
then you may not be able to open it until you upgrade.
If you have xl95, you won't be able to open a workbook saved in xl97, 2k, 2002,
2003 file format. But xl97 should open an xl2k, xl2002 or xl2003 workbook with
no problems.
(and xl95 could open those workbook if they were saved in xl95 (or combo
fileformat)