mp3/wav wav/mp3 converter

Check the www.zdnet.com download secton.  They have many converters and if no "free" ones, there will be some that have trial versions that will do it for a limited time. 

http://audacity.sourceforge.net/about.php

Audacity is IMO the best audio converter/recorder/editor out there, and like most excellent programs it's FREE!!

you can also try CDex - http://cdexos.sourceforge.net

it's mainly a cd ripping program but it does mp3 <> wav conversions also