Hi Duncan,
Since my question here, I readed many opinion on many forums and I concluded that I will keep my Quicktime to the version 7.3.1 that is correct for Final Cut 5.1.4 and my system 7.4.11.
I made update to my iPod Touch (2.2.1)(iTunes 8 and Quicktime 7.5.5) on a PC not on my Mac !
However I readed that some are no problem with the Quicktime update with FCP 5.1.4 but not enough for to ‘push’ me to update mien !
Daniel