Well, if you are looking for mp3 support on your system you will also have to install an extra xmms component because the xmms rpms in Fedora and Red hat will not allow you to play mp3's right off the bat.
The easy way to take care of this would be to use yum to install the package named xmms-mp3 (or something to that effect). If that is the wrong name for the package you can also use yum to search the contents of the repository for any package with the terms "xmms" and "mp3" in its name and then read the description. If the description is the right one, then you know to use that package name to install mp3 support for xmms.
In the event that all of this fails for some random reason, just install Audacious media player. It basically IS xmms, except it has been updated and ported over to GTK 2.0. I like it pretty well and I haven't gone back to XMMS since i first started using it.
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