First of all get fedora 13!!
second "yum install gstreamer-plugins-ugly" will install you codecs(decoders, the thingy that transforms computer data into sound) will be installed. But this isn't in default fedora repository because mp3 belongs to somebody and that asshole want everybody to pay for using it, since there is copyright problems they cannot add it to default fedora repository.
Enable the rpmfusion repository(google it, enabling is very easy!), and do "yum install gstreamer-plugins-ugly" also f13 comes music player called totem, you can also install other player with "yum install <player name here>" for exampled if you wanna install VLC player type "yum install vlc" and it automatically installs
Good luck and welcome to linux
also;
http://www.mjmwired.net/resources/mjm-fedora-f13.html
this link is a fedora beginners bible, explains how to install lots of stuff, including mp3 codecs players, flash player, media players, truetype fonts, Java RE, acrobat reader even samba.