I created a one-second movie using the QuickTime 'DVCPRO-PAL' Apple codec. If you attempt to play it with QT Player 5.0.2, you should get the standard, "QuickTime does not have the necessary software . . . " message. Then QT Updater should launch and download the new 'QuickTime JPEG Update' and 'QuickTime DV Update' extensions.
This should work for both Classic and OS X. Just play the movie with each version of QuickTime Player. In Classic, these will appear as extensions in the System Folder -> Extensions -> QuickTime Extensions folder.
This seems to be the only change in QT 5.0.4. These are the same components included on the new FinalCut Pro 3.0 installer CD.
[Editor's note: It appears this movie has been pulled from the referenced webpage. I'm leaving the article here as some of the discussion below contains useful information.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020103171405982