You also have other options. For example, go to LW's preferences & choose Plugins, MIME & select all. Go to update & tick intall new 3rd party plug ins. Also go to DivX go to http://www.divxmovies.com/codec/
For 3ivx go to http://www.3ivx.com/ & go to dwnld page & look on top right of page.
I should also have mentioned Xvid which you'll find at the divx site I gave you.
There's also other players you could try such as VLC: http://www.videolan.org/vlc/ (choose nearest mirror site)