Go into DiskUtility and select your drive and click Repair Permissions. DiskUtility is in the /Applications/Utilities folder.
I'm pretty sure Jaguar(10.2) has the same Repair Permissions option as Panther(10.3) does.
If not, start up from your OS X install CD, and select the DiskUtility from the menu at the top once it has booted off the cd. Then select Repair Permissions on your disk.
If that doesn't work, try opening your system log file:
Open the Console app from /Applications/Utilities. It should open console.log.
If not, select the file menu and select Open Console Log.
Look for anything that has to do with iTunes and reply with what it says in the log here.