Check out this site for info all about fedora and how to install things. http://stanton-finley.net/fedora_cor...ion_notes.html
For mp3 to work you need to install the xmms-mp3 rpm. Do a search here or on the above link on installing this. mp3 is a non open source compresssion and requires a fee to use in a program to program basis. So for legaliaty issues it is not installed by default under Redhat/Fedora. I believe this is writting in the release notes. Check them out to learn more about your relase of Fedora. I thought xmms is normally installed by default but may depend on the install option you selected. The rpm you need for xmms is on one of the install CDs. To see if it is installed run this command in a terminal console session.
rpm -qa | grep xmms
If it is not listed then you will need to install it.
As root goto the cd that has the xmms.*.rpm and run this command.
rpm -ivh xmms*.rpm