RSS feeds are meant for feeding headline-type information, not the sort of bulk information delivery that would be typical of a catalog. Announcements of newly available products, for instance, or, as trippleweb says, items on sale, items back in stock after a long wait, articles about new uses for existing products... but not the catalog itself.
http://www.xml.com/lpt/a/2002/12/18/dive-into-xml.html and http://en.wikipedia.org/wiki/RSS_(file_format) are good references that explains (at least in its first few paragraphs) what RSS is good for.
http://www.eopta.com/spec/rss-tutorial/ and
http://www.packtpub.com/files/RSS_an..._newsfeeds.pdf also look interesting.
But it sounds like you need to do some more research on what RSS is and what it isn't, and other different ways you can publish a product database (in an excel sheet or whatever other format) as a group of Web pages.