I don't know if iTunes can play ogg files. A quick search reveals that there is a plugin (http://www.macosxhints.com/article.php?story=20021103065300430) for iTunes that will let it play .ogg files. I'm kind of shooting in the dark here as it's been a long time since I used a Mac. Last time I used one, it was an LC II running OS 7.
Re: Why "ogg" files...?