At any rate, it sounds like the OS is fine but something in your user account is cattywhompas! Else the other accounts would have the same problem.
Umm, ... the other accounts do have the same problem...therefore I conclude that the system itself is wonky.
It's only if/when I boot to a backup drive/partition that I get normal/full functionality.
I'm thinking of overwriting the older backup w/ a copy of the newer backup as a 'safety' copy, then update iTunes [I think the QT update is required as well], and at some point the 10.5.4 upgrade, and work on carefully 'reconciling' certain data files and folders on the main boot drive w/ the more functional OS files on the backup partition w/o re-introducing the source of the wonkiness.
Oh boy! Sounds like loads of fun!!