The new iTunes (4.5), as others have noted, is less than perfect. Which is sad, because the previous version pretty much was. Thanks to the guys at the OS X LiveJournal community I managed to get 4.2 installed in place of 4.5…. but 4.5 changes the iTunes library format, so 4.2 can’t read it and quits on startup.
On a totally unrelated Mac note, if you have HDTV and a Mac, you’ll want to check out this little hint.