A few weeks ago I had to read and write Excel files of the format BIFF8 (Excel 97), because the customer did not accept the workaround of exporting data to CSV.
PEAR's Spreadsheet_Excel_Writer combined with the project Spreadsheet_Excel_Reader on SourceForge was a good helper in the past - but only for BIFF5.
BIFF8 support in spreadsheet excel writer has been a problem for a long time, and according to the authors, is still somewhat kludgy in the current version.
So I needed an alternative.