Hi Jim,
Winamp is one program that will do it for ya. If you don't have it, you can get it at
www.winamp.com.
To change the file into .wav in winamp go to Options/Preferences then to plug-ins, to Output and doubleclick on the Nullsoft Disk Writer plug-in. The file will be turned into a .wav file when you play it. After you're done just change it back to Nullsoft waveOut plug-in.
That's one program, cdex will do it for ya two, both ways (mp3 to .wav and .wav to mp3(winamp can't turn .wav's into mp3's, maybe with an additional plug-in, I'm not sure).
The url for it is:
http://cdex.n3.net/
Both programs are free.
HTH