To add to the previous comments:
The converter for opening .ods files in Microsoft Excel 2003 is very clumsy to use. You need the Compatibility Pack and then you need the Converter on top of that. I don't know how well it converts formulas, especially for the most-recent versions of OpenOffice.org and LibreOffice. I definitely don't recommend this path for Office 2003 if you need to return an .ods.
Another solution is to use either of OpenOffice.org or LibreOffice.org to open them. Both have Save As ... Microsoft Excel 97/2000/XP (.xls) that is usable in moving the spreadsheet to Microsoft Excel if that is where you need it. If you just want to view and use the spreadsheet, you should use one of those applications. LibreOffice has more-recent releases while Apache OpenOffice won't produce a successor to OpenOffice.org 3.3 until farther into 2012. It's your choice.