I essentially have all of the latest updates for the Ubuntu 11 Natty OS. I've installed media players and plug-ins and the latest Adobe Flash Player. I could install some media player plugin-ins while others I couldn't. I cannot figure out what else to to. Please help.

My Firefox 4 add-ons are:
Adobe Reader 9.4; DivX Web Player; DivX Browser Plub-in; IcedTea Web Plugin; iTunes Application Detector; mPlayer (Gecko)media player plug-in; QuickTime plug-in 7.6.4 & 7.6.6; RealPlayer 9; Shockwave Flash; VLC multimedia plug-in; Windows Media Player Plug-in and Windows Media Player Plug-in 10

My media players are: Totem, GNOME MPlayer; SMPlayer
My music players are: Banshee; Rhythmbox; GMusicBrowser.