You can mix to wave or ogg from RiffWorks and then convert either format using an external program like Audacity (Free Download) or similar. Welcome aboard my friend.
Uncle Bill
No-one remembers what you do or say. Everyone remembers how you made them feel. Allegedly !!!!
If you use Audacity.....make sure you also download the LAME mp3 encoder....you'll see it there also.............with instructions how to install...........
ITunes works well but Audacity can be used for a lot more then just conversions.........I use it as the last step in mastering on almost all my tunes..........