I know that there are a variety of programs that will do that for you. DBPower Amp is one of them but do consider the fact that you will be converting one format which is compressed into another format which will compress the file once again. If you have the CDs that the music came from (obviously you do
) then I think that the quality will remain much better if you re-process the tracks from those CDs.
I would try converting a few tracks from WMA to MP3 with a free or trial version, and then see if that produces a decent quality. If you're happy with the quality you can always do the rest as well, if not then dig out the CDs!
Audiograbber is a great free CD-ripping and MP3 converting utility but I think that it is not able to process a WMA file directly. If you Google 'WMA to MP3' you will get lots of hits, popular download sites will also be able to provide some useful bits of software.