I use C-Dex. You can find it here -->
http://www.cdex.n3.net
It lets you go from MP3 to WAV and vice versa. It also makes it easy because you can do whole blocks of files all at once. So if you want to make a CD for the car you can just put all the songs in it,convert them and burn them all at the same time. I have heard that some other programs make you do them one at a time.