Creating an Excel File without Excel
Check out something that I created a couple of years ago called Creating an Excel File without Excel. The last and only time (2002) that I went to LotusSphere this came up in one of the sessions that some people where looking to create Excel files on the AS/400. Maybe someone can still use it.
It it actually quite a bit easier now then it was back then.
You can create a file useing plain old HTML, slap an xls extension on it and excel will read it just fine. With newer versions of excel you can generate xml and do a full fidelity spreadsheet, multiple sheets, whatever.
All without any special libraries.