You can try to capture rtmp:// .flv streams from
Napster in real time while you listen to them using freeware
CooJah (without Blader) or shareware
Replay Media Catcher in the RTMP recording mode.
Replay Media Catcher allows you to extract MP3 and AAC audio tracks from captured FLV files as well. So you don't need to convert anything and won't lose quality of your recordings.