I'm having exactly the same issue OS X 10.2, G4 Desktop. The only thing I've installed lately is Itunes 6. I've repaired my permissions (using the tool and by restarting in OS 9 and removing my preferences folder) nothing working! If anyone has a solution to this please say!
Then unfortunately, you've got a real problem on your hands.
My first suggestion, if you're using Norton Systemworks or any other piece of crap brought to you by the fine folks are Symantec, disable and uninstall it as your first order of business. Are you using anything like that?
Problem's still there, and itunes has now stopped working. Click on play and it looks like it's going to play but the track doesn't count down and no music plays. No idea if it's related but it feels like everything is going wrong!
This should return EVERYTHING on the Mac that has the word Norton in it.
Otherwise, you're quickly getting to the point where about all I can suggest is a complete reinstall of the OS. We're nearing the point where troubleshooting via forum isn't practical and a reinstallation is faster/easier. The fact that this problem follows you to a new account clearly indicates that it's system wide. What it could be, I'm not sure as I've never had this problem with any of the Macs I support, but in everything I've ever read, some POS from Symantec is responsible.