First order of business. You will not be able to run some of Quicktime 7's audio through your Digidesign Hardware until Digidesign releases a fix. Most likely a new version of Core Audio Setup for OSX 10.3.9 users. Much the same way you can't run your Digidesign Hardware and Pro Tools on OSX 10.4 Tiger until Digidesign releases Tiger updates for Core Audio and Pro Tools. This does not mean you can't run other audio related apps. Just not QT 7.
Here are my findings on dealing with this bug.
1) Those who would like to run Quicktime sound through their Digidesign Hardware must re-install Quicktime 6.5.2 you can do that here http://www.apple.com/support/downloads/ ... ormac.html this re-installer will remove Quicktime 7 and re-install 6.5.2. This will also work for those who upgraded thinking they could use their Quicktime 6 Pro serial numbers to get Quicktime 7 Pro.
Anyone who wishes to continue to run QT 7 and doesn't mind that you won't be able to hear it's sound via your Digi Hardware in certain uses simply skip to the next step.
2) Install Digidesign's Core Audio Setup 6.9. Here http://www.digidesign.com/ under downloads you'll find Core Audio Setup 6.9. This is the most recent version of Core Audio Setup Available as of May 15 ,2005. This goes for users of all versions of Pro Tools LE 6x that have previously run on Panther OSX 10.3.9 with the MBox, Digi 002Rack, and Digi 002. This also goes for Digi 001 users (of which I am one). While Digidesign does not officially qualify the Digi 001 for use with OSX 10.3.9 or Core Audio Setup 6.9, it works fine. I am listening to the Beatles White Album right now through ITunes via my Digi 001 on OSX 10.3.9 using Core Audio Setup 6.9. Your system will not crash and you won't lose Pro Tools forever. This should be a total fix for MBox, Digi 002 Rack, and Digi 002 users. Some Digi 001 users may continue to have problems which I'll address in the final recommended step, however I reccomend exhausting these two steps before going there as it is A LAST RESORT.
3) Again A LAST RESORT. I find this is only necessary in some rare cases where folks are using older model Apple computers and the Digi 001. Backup your files and re-install your OS and apps. I recommend not upgrading beyond OS X 10.3.8. You'll be better for it as your Digital Audio Workstation will be more stable. If you do, obviously don't install Quicktime 7.
Hope this is helpful. Now in the words of Michael Pare in "Eddie & The Cruisers", "Let's get on with the music."