FWIW, I find the QuickTime codecs to bt much better than VLC or MPLayer, especially on slower hardware. 3ivx has always been the king of speed, but unfortunately it has some issues with Tiger than have yet to be resolved. Divx 6 has gone a long way to close the speed gap, though, and I feel it's significantly better than the non-QT options out there.
Plus, the other players don't give you the features of QuickTime. No editing ability, no fast forwarding (skipping ahead 5 seconds does not count), no decent scrubbing, no variable speed, no bass control....the list goes on and on.
I definitely think it's worth the effort to get things running in QuickTime whenever possible. I love VLC and MPlayer, but really, they're last resorts.
Since you say you fixed the sound, I guess you must already have something installed. What is it? If you already have Divx installed and it still doesn't work, I'll need more info on the movie.