if you're planning to ply mp3s on xmms(mp3 player for linux), then you should download a plugin for that. the plugin is needed to play mp3s.. search for xmms mp3 player plugin..
as for your internet connection, if FC3 didn't detect your modem as a generic type, didn't detect at all , then I suggest you search for drivers. But before you do that, try taking your modem out, boot your FC3. afterwards, turn it back of, put the modem in, then boot, in this way, FC3 can show you a message if it found your modem or not.
I will also suggest google for some support on this.
dude..another thing.. I'd lke to invite you to join www.corehackers.com..you
'll learn a lot about linux from there.