Lorma linux 4.0 is a Distro based on Fedora Core 1 ... it contains MP3 support out of the box for XMMS, ... looks like mplayer is included as well. Here is an article from OSNews.com. Here is another good article from cahtech.
The good is lots of multimedia support
... the bad is that there are currently no update (errata) download repositories
I may install this as a test on a spare hard drive ... If I do, I'll post something here.