I had to work through this myself recently. This works for me.
A little utility called vsound will capture any OSS audio stream to a wav file.
Realaudio capture goes like this: "vsound -f whatever.wav helix-player -q whichever.ram" (with Real codecs in the appropriate place, of course) produces a wav file from the RA stream. Use lame or audacity to convert to the audio file format of choice.
(watch your assumptions.)