playing .ogg on Macs

It depends on which OS version you're using.
In Panther with quicktime 6 you can play oggs
using a 3rd party plug in.
Unfortunately, Tiger and quicktime 7 "broke" the ogg
plug-in and it hasn't been updated yet.

Nonetheless, you can listen to (and edit)
.ogg's using Audacity, which is an open source
audio editor. It's freely available and fairly
easy to use, though it is a full audio editor
and not just a "player." It will also convert
.oggs to whatever format you desire.

http://audacity.sourceforge.net/

--Bill Sethares