Excel – Converting Excel 2007 files to Excel 2003

I'm currently using a library named http://www.codeplex.com/ExcelPackage>ExcelPackage to generate a large number of Excel files.

Unfortunately it saves in an xlsx format, the Excel 2007 OOXML format. I need it in the earlier 2003 .xls format, for my clients who tend to be somewhat technophobic when it comes to upgrading software. This basically means I can't make the end users use any sort of compatibility software like the official MS one. I can only convert the file, or use a completely different option, but it must result in a Excel 2003 readable file.

Is there any way I can either use another library to write it in the appropriate format, or find a library that will allow me to write autoshapes and the like directly into a 2003 format file? Using CarlosAg's http://www.carlosag.net/Tools/ExcelXmlWriter/>ExcelXML method does not allow me to easily insert images.

In the end, I used http://www.nika-soft.com/nativeexcel2/ to power the conversion to the earlier version. This library, while not free, was very simple to use and worked precisely as advertised.