Hi
I would suggest you don't, mp3 is not a free codec, it is an excelent
example how patents on software and algorithms hinder open source, you'd
better use ogg/vorbis-tools/oggenc instead, download, compile and
install bladeenc or LAME yourself if you insist on mp3.
Using flac is also an option for those who dont want to use lossy formats
regards Rahul