I dug out my DVDs from SIGGRAPH 2003 and 2004 today, and the movies no longer play.
I went to Techsmith's Camtasia site and downloaded and installed the latest QuickTime
component for the Ensharpen Codec (1.2) for my Intel Mac, but no luck. I've done the
restart, repair permissions, etc. to no avail.
Has someone posted a solution to this in this forum in the past, perhaps?
(QuickTime 7 Pro, Intel Mac).

Hmm... I don't think so.
Installing the Ensharpen codec has always worked.

I'm wondering if there is a way we can update/convert the tutorials and share them with a new generation of A:M users.

I'll check and see if I've got the same videos handy here.

Solved.
The problem was a conflict between Camtasia's Ensharpen codec and the Perian video extension.
That conflict has been resolved in Perian 1.2, the newest version.