I recently installed iTunes 2.0.4. As per the Read Me, I deleted the application and its Dock alias first. I also removed the iTunesHelper app from the Login Items pane of the Login System Preferences Panel, assuming that the iTunes installer would put a new one in its place.
It didn't, however. So how to get it back? I knew the iTunesHelper was hidden in the iTunes.app package, so I couldn't access it through Login's Add... button. I originally thought I'd just create an alias to the iTunesHelper and add that, but in the end I didn't need to. Just dragging the app onto the Login Items list is enough.
So, Show iTunes' package contents using the Finder's contextual menu. Navigate to the Resources folder, find iTunesHelper and drag it to the open Login Items pane. Done!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020327235526419