One of my personal favourite programs for converting audio from one format to another is dBpowerAMP. It is simple to use and more importantly uses many different audio codecs:
dBpowerAMP supports practically every audio type created: mp3, mp4, m4a, wma, Ogg Vorbis, AAC, Monkeys Audio, FLAC, the list goes on….fully compatible with Windows 95 / 98 / ME / NT4 / 2000, Windows XP. Split into four components (no need to bloat your computer, install just what is required), all functioning seamlessly together:
Remember though, when converting audio that it is best to convert from an original wave file (uncompressed format). Converting from one compressed format to another (MP3, WMA, Ogg etc) can have undesired and poor results.