Simple Media System (SMS)
SMS is a Media Player for the PS2. It can play DivX/XviD movies with different screen resolutions and encoding methods, includes support for network files, USB drives, hard disc drives as well as the disc drive. It now also allows subtitles to be displayed, and contains a fully functional MP3 player.
Here are places you can get info on using SMS:
User Manual - In-depth guide to using SMS
SMS Official Forums - You can ask questions or make suggestions here.
SMS Homepage - The author of SMS's website