Have you checked for updates from Nero's website? Which version of Nero do you have? Here's some nero links 1. http://www.nero.com/nero6/en/Support.html
_ 2. _ http://www.nero.com/nero6/en/wma-plugin.php
_ 3. _ http://www.nero.com/nero6/en/Updates_prev.html

There's only 2 types of mp3 I'm aware of. One is mp3 & the other is mp3pro. Except for a very rare type that allows for higher than 320 kbps bitrate. Other than mp3, there's ogg vorbis, m4a/mp4, & wma & rp.

It will still probably be worth getting the codecs pack. Check the audio codecs at the top left here http://www.free-codecs.com/
I'm not sure whether nero requires its own codecs or not.