Okay, now what? I went into the File Exchange Control Panel and couldn't find a way to change Translation Preferences.
Under FILE TRANSLATION, all I could do is "Add..." or "Remove" items. I removed SoundJam and MusicMatch Jukebox. Under PC TRANSLATION, the application is set to iTunes already and there is no mention of SoundJam or MusicMatch Jukebox.
Still, when I double-click an MP3 file created by one of those apps, it my Mac uses those apps for playback instead of iTunes. Is there a way to change all MP3 files on my HD so that they open with iTunes?