The short summary

You only need to install this rpm to be able to play mp3's in RedHat 8:
xmms-mpg123-1.2.7-13.i386.rpm

Complete set of xmms rpm's for RedHat 8

This is a set of RPM's for RedHat 8 that includes the mpeg audio input plugin. Redhat 8 shipped without support for mpeg audio due to concerns about patents. In able to easily be able to add mpeg decoding to a RedHat install, these RPM's are built with the RedHat spec file. The RPM's that are distributed by xmms.org are a bit different.

Source:

xmms-1.2.7-13.src.rpm

Binary packages:

xmms-1.2.7-13.i386.rpm
xmms-mpg123-1.2.7-13.i386.rpm (mpg123 plugin)
xmms-skins-1.2.7-13.i386.rpm (skin package)
xmms-devel-1.2.7-13.i386.rpm (devel package)

Håvard Kvålen <havardk@xmms.org>