There are quite a few audio converters out there but, like Bill points out, Audacity will do it (and for free!). Just make sure you download the additional plugin to allow .mp3 conversion to happen.
Scott recommended Audacity to me sometime ago and it’s been a great tool. I was a bit concerned when I upgraded (please down laugh) to Vista but Audacity continued to preformed well. It’s got a ton of the other features which I wish I had time to familiarize myself with.
If you guys have a Creative sound card you might already have a wave to mp3 conversion tool. Creative audio converter. I like it because I can convert batches of files and specify all the bit rates save locations and its very quick.