Create App That Converts File Structure to XML Files

Flash Media players require associated XML text files that contain HTML code. This code tells the media player category names, filenames, and file locations. The job is to develop an application that will read a file structure of media files, and generate a set of XML documents that will properly drive the Flash Media player. This app must be PC and MAC OS X compatible. I am not sure what language this would best be written in. Please advise.