XMMS is a Winamp style multimedia player for Linux. It plays MP3 files just fine. However, if you installed a version of Redhat linux, or a distro based on Redhat, you got a crippled version of XMMS that won't play MP3s because Redhat is worried about being sued by the RIAA storm troopers. You can easily fix this problem by downloading and installing a new version of XMMS from
http://www.xmms.org/.