I always used a program called "Blaze media pro" for converting stuff. It lets you convert between MP3, WMA, WAV, and OGG if I remember right.
It also lets you convert video files between the various codecs you have installed. Shame it's not freeware, but it's a 21 days trial that never expires, so it's almost free
I don't know where to download it, I got it from a CD in a computer magazine, but I'm sharing the file on WinMX, so come to the WinMxWorld.Com chatroom and ask me if anyone wants it