Unfortunately to use yum the way megerdin suggested would require an internet connection.
Go here: http://download1.rpmfusion.org/free/...w/M.group.html
Grab the three mplayer rpms. Then do a 'yum localinstall mplayer' from the same directory that you have the rpms you downloaded. This will probably produce a list of missing dependencies that you will have to go back and download. You may have to go through several cycles of this as most modern distro will assume you have a net connection.
You are aware that all support for F8 will be dropped in early January (7th?)? After that there will be no updates of any kind.