lol, i asked the same question when i was a newb, the advice given to me was...
instead of messing about with pluggins, use a media player that was specifically designed to play whatever you wanna play.
and the answer is.... mplayer !
mplayer is reealy the best most compatable media player for linux,
mplayer is to linux, as winamp and windows media player is to windows.
download the following files...
and bring up a comand line console...
cd to wherever u downloaded
rpm -ivh mplayer-*.rpm
that will install mplayer + mplayers command line interface, and mplayer's graphical user interface.
issue the command gmplayer to load the media players graphical user interface, or the command mplayer (media_file) to play from cmmand line.
with that installation you can play almost ALL media types...
and, if you wanna play the scary media trypes (like quicktime) download the win32 codecs from the same site.
will give more information.