Cool - I couldn't find the package xmms-mp3, maybe my repos are fucked.
try dag... create a file /etc/yum.repos.d/dag.repo with the following in it. You'll have to go to dags site manually to get the GPG key or just disable the check.
[dag]
name=Dag RPM Repository for Fedora Core
baseurl=http://apt.sw.be/fedora/$releasever/en/$basearch/dag
gpgcheck=1
enabled=1