What is the best way to open ods files in Excel 2003?
Is there some plug-in available? Should I use some convertor to xls? Or would it be best if I just used LibreOffice (or OpenOffice)?
The file I want to open shouldn't contain anything fancy, so I probably don't need a solution that understands every detail of the format.
Using OpenOffice is probably the easiest option IMO because there's no file format conversion necessary and OpenOffice is freely available.
There is a BSD licensed Microsoft Office 2003 plugin that is available, OpenXML/ODF Translator Add-in for Office. I don't have Microsoft Office so I'm unable to try it.
Would it be best if I just used LibreOffice (or OpenOffice)?
Yes, it would probably work best if you just used Libre/OpenOffice. As much as OpenOffice does a good job of viewing Microsoft files, it doesn't do a perfect job. Sometimes there will be little differences (more noticeable with word documents), so it's always best to use Office for Microsoft files and OpenOffice for the open formats. But once you do that, you can save it as an xls and then it should open in Excel 2003 just fine.
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.
If your files do not hold sensitive data you can upload the ods file to Google Drive. Afterwards open the file as spreadsheet, then use the top menu to download the file as XLS or XLSX. Google does the conversion for you.
Disclaimer: I could not open some files in Excel 2003 after conversion. If you run into the same problem, open the spreadsheet in Google Drive, mark all cells, copy, paste them into a newly created spreadsheet. Downlaod the new spreadsheet, then it works.
