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It's hidden in the package contents of OS X installer. And the audio and video of the movie are separate. :(

I just love that video. But it's all over YouTube, and you can watch it again and again. ;)

EDIT: BTW, I like the Tiger intro music a lot better.
 
I stole this from the original poster (John Greythorne) on the SonikMatter website.

Go into the "/System/Library/CoreServices" folder and control-click on "Setup Assistant". Click on "Show Package Contents".
In the package, go into the "Contents" folder and then the "Resources" folder. Control-click on "TransitionSection.bundle" and click on "Show Package Contents".
Again, go into the "Contents" folder and then the "Resources" folder.
You'll find the "intro-sound.mp3" and "intro.mov" files there.
 
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