Blizzard uses divx codec for their in-game cinematics in Warcraft III. That's what it's got to do with it.
I did install the latest divx, but it didn't help a lot. I found two other work-arounds though (for some arbitrary reason Warcraft III seems to conflict with the divx qt-components on Intel-based Macs):
a) After you install divx, remove the 'divxEncoder.component' and 'divxDecoder.coponent' from '/Library/Quicktime/'.
You won't of course be able to watch divx movies using quicktime, but Warcraft will work with cinematics and all.
After you launched Warcraft once, you can put back the codec files. When you launch warcraft again, it won't try to play the introduction sequence again and you can play, though it will crash if another cinematic is played during single player campaigns.
b) Rename or remove the folder 'Warcraft III Folder/Movies'
That way, all cinematics will be skipped and warcraft won't crash when it try to play one. Plus, you get to watch divx with Quicktime/iTunes 😉
