Pretty much mplayer is for video files, but can play audio as well. If you are used to winamp(2.x versions) and don't want to forget the wonderful times, having xmms is pretty much identical in usage and looks. I have never had either mplayer or xmms not come standard in the distros I have used yet so they should be easy to install off of the distro's ISOs if needed. Also another good video player is Xine, which is pretty standardize by now. There really is no need to have both Xine and Mplayer installed at the same time since they do the same function, and they do it well. If I had to compair the two their really is no big difference in feel, it is basically comparing KDE to Gnome. They both have their specialized features but in the end they both are winners.
Thats my two cents for today