From your status I guess that you know about the platform-independency. The only way I know to read Excel-files is with a Micro$oft Server and Office installed and I heard that it is also possible if you have Openoffice/Staroffice installed on your server. Eather way it is difficult to make the access. Both ways work with APIs. I think in Openoffice you have to internally (on the server) convert the file first to an Openoffice file and then you can access it.
This is the reason why I always tried to get around that stuff. If you only want to create Excel-files, it is much easier, because PEAR (pear.php.net) has a module for that.
Grisu
