Okay, the best part about this is that when it comes to licensing out their songs, Led Zeppelin is super SUPER proprietary. You’ll probably have noticed that despite the fact that Dean is OBSESSED with Zeppelin, and that there are so many Zeppelin references in the show (there is even an episode named using the lyrics of this very song) they still have yet to use one of their songs on the show. Anyways, long story short, in order to have permission to use the Immigrant Song, Jack Black had to make a video which they sent to the band, in which he literally got on his knees while wearing the AC/DC school boy outfit he wears in the final scene of the movie, with a crowd of screaming people behind him, just begging them to be able to use the song.
And it worked.
I want to hear that story as a bedtime story every night.