Recording from "Built in" to MP3 in OSX


hey guys- anyone know if you can record (preferably direct to MP3) from "built in" in OS X- ie anything the soundcard is playing. You used to be able to choose "built in" in OS 9 as a recording source and programmes like Sound Jam could encode MP3s as it recorded. I can't seem to find anything like this for OS X. Any ideas much appreciated!!!