While not specific to WordPress I get this question often because this topic is new for many small churches. But not totally new since most churches have sound systems that have been set up for capturing sermon audio to tape. Though when you start talking about MP3's and sermon podcasting and the like, it gets confusing.
WordPress as a CMS and plugins that help
ThemeShaper.com has a good article on using WordPress as a CMS and lists a few plugins that come in handy …