well,
the question is in the subject!!
this may have bben answered in another topic, but I have a very slow connection and don't have money and time to search for it!!
i use mp3 audio, anyway not from NLE. what i do normally - render the entire timeline to a HiBitrate DivX + uncompressed audio file. Then I can recompress it in VirtualDub to DivX + mp3 or to wmv video.
The only problem with audio comression imho is weather the one 'll be available on client computers. wma and mp3 are ok, real audio (and video), ac3, ogg and other require a codec installation to be distribuded together with video.