If you're using files that you haven't recorded yourself, you may want to look in to whether or not it's okay to publish them to the web. You may also want to learn about what it means to copyright your own work. Here are two organizations that will help you learn about copyright issues as they pertain to digital media.
Electronic Frontier Foundation (http://www.eff.org/mission.php)
Creative Commons (http://creativecommons.org)
Both organizations have information specific to podcasters.
Publishing your podcast