The QuickTime 7 upgrade wipes out your Quicktime 6 Pro without notice or permission. Here's how Apple customer service told me to get it back:
Previous versions of QuickTime, including a reinstaller for QuickTime 6, are available from Apple's QuickTime support page.
[robg adds: This reinstaller only works in 10.3.9; 10.4 requires QuickTime 7.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050524112528287