Burn the tracks into a CD as regular audio tracks, then re-rip as MP3 using LAME.
There will be a loss of quality due to the re-encoding though.
Alternatively, you can loop the sound via line in (or if you have an X-Fi, use the record 'what you hear' option in the Audio Creation mode console) and record the audio via Audacity, and then re-encode. Again, there will be a loss in quality during re-encoding.