Due to licensing restriction, Fedora does not have mp3 support. They recommend you use OGG.
However, I was able to play mp3 files by installing a simple program called xmms. Open a terminal, type yum install xmms and it will automatically download & install it for you.
I've noticed you're running an old version of Fedora. If you have the time and bandwith, I strongly recommend that you upgrade to Fedora Core 5 because version 1 isn't supported anymore.