Create XML Feed

We need a xml feed created. The feed will pull data from an inventory database. The feed will provide data to a third party online classified site. The inventory is in MySql format created by a php shoping cart file. We already have a php file that creates a text file version. The xml file needs to create the same output. We can provide xml feed details providign by third party, access to MySql file, and a copy of the exisiting files.