If you are going to create a standard audio CD, then Nero will do so automatically. Simply select Make Audio CD from Nero StarSmart, add your MP3 audio files, and any other formats such as WAV, VQF, WMA, etc and Nero will convert them to the proper format automatically.
If you simply wish to convert them to WAV and store them on your Hard Drive, this can only be done with the Retail version of Nero 6 Ultra Edition. The OEM version does not support this. The OEM version can only RIPP audio from an Audio CD to your Hard Drive in WAV, MP3, VQF, WMA, etc, but can not convert an existing audio file to another format.