Hi Floh,
I got the legacy QT codecs (at least the Media 100 ones-haven’t tried any others) to work under 10.6.8.
I deleted ALL the Quicktime files I could find (anything that had QuickTime or QT in the name).
Installed QT 7.6 from the Install Disc for my MacBook Pro 17″ restarted and it worked. I can use the old Media 100 files in FCP 7.03 and they show up as actual video clips – that need some rendering of course. When I first did the re-install, I tried the videos and they didn’t work, but the restart fixed that.
Not sure if this was a fluke, but it is still working for me.