Sure, first things first, remove the realplayer rpm package(since it is not working) by typing something like;
rpm -e RealPlayer
Second install the rpmforge-release package as directed here; http://dag.wieers.com/rpm/FAQ.php#B
When done type: yum install mplayer mplayerplug-in xmms xmms-mp3
Mplayer is all that your really need it will play mp3 files just fine along with other audio/video formats. The mplayerplug-in package is mainly for watching videos from the Internet, the xmms packages allow playing of mp3's and other audio formats, it is similar to winamp.
One can also install xine (another audio/video player) and/or VLC along with or instead of mplayer using yum;
yum install xine vlc