Please refer to Microsoft.Office.Interop.Excel.XlFileFormat enum to understand the file formats while saving the document. Choose the one that maps the 97-2003 type and use that while saving. Hope this helps!!
Thanks
Arun
Hi twl,
With regards to using the Open XML SDK, you can't save as a .XLS. After creating the .XLSX, you can use Excel automation to open the .XLSX and save as .XLS. If you have the capability, you can use Word Automation Services to convert a .XLSX to .XLS.
Also see: What is the difference between Word Automation and Word Automation Services.
If possible, users of Office 2003 and Office XP can install the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint File Formats. This will allow them to open DOCX files directly.
-Eric