Sonique PLS Files
If you are working with a radio station that uses PLS files, these are the extension used by Sonique for its playlists.
ShoutCast uses PLS files, for example, for its playlist for a given radio station. When you connect to a station's PLS file, you are in essence downloading their playlist and then working through the songs one by one.
Sonique is shareware, and is available for free from www.sonique.com.
Music File Formats
Music / MP3 Tips and Information