Ok, I searched around, I found nothing, so I am sorry if this has been mentioned before:
How do you play custom ogg files in Vendetta?

And furthermore, could someone please locate me a free Mac OS X compatible ogg encoder?

Two ways to play your own .ogg's are /playmusic filename.ogg and /playlist playlist.m3u

Theres no way to randomise them, or skip tracks in a playlist or any such thing, so running a media player in the background is usually better than using the built in .ogg player. (one instant benefit is more formats supported)

I don't have a mac, but this page http://xlr8yourmac.com/audio/issue71.html this page http://www.nouturn.com/ and this page http://www.google.co.uk/search?q=mp3+to+ogg+mac+os+x all seem to have info :)