First, you need to setup Medibuntu as one of your repositories because you can get most update from it. Installation and setup note should be available in their website. After, add it to sources.list file, do the following command in Terminal. (you can use other GUI players instead of smplayer)
sudo apt-get install vlc mplayer mozilla-mplayer smplayer w32codecs
I, also, recommend uninstalling totem.
sudo apt-get remove totem totem-common
totem-gstreamer totem-mozilla totem-plugin
After finishing install, Smplayer can play a movie mediately, but it requires a little configuration for Firefox. Finding some video test page, I google and use this page. In my computer video doesn't show up, I have to change video output to x11 by right click on grey background -> configure -> x11 from Video Output drop down list. Done, you have nearly perfect movie player with Ubuntu Intrepid.
 - https://help.ubuntu.com/community/Medibuntu
 - http://home.att.net/~cherokee68/wmvtest.html