Sorry that should have read
'...when CS5 is installed...'
On the PC side in those situations it is advised to deactivate CS5, uninstall, install CS3 and then reinstall CS5. If you don't, your registry entries will become corrupt and you lose dynamic linking capabilities, etc.
First the old software, then the new software. I guess it is the same on MAC's.
Thanks - kind of expected that : )