The "classic" method, would be to use
Total Recorder to rip the sound data as it goes to the soundcard.
The CHEAPSKATE ( =free ) version, is to do loopback recording, with the record sorce set to be Wave/MP3, "Stereo Mix" or "What-U-Hear" - this re-digitizes through the soundcard, but probaly won't make a lot of difference to streamed audio.
BEST method, if you want Radio one, would be to get a device such as the PSION Wavefinder, and record off DAB - with no strain to your net connection.
PS. A tool called "Streambox ripper" may be able to help you rip a real stream directly, but it's an illegal tool ... hit the search engines and you may find it.
http://www.sonicspot.com/streamboxripper/streamboxripper.html
The full situation being that versions of Streambox ripper and Streambox VCR that supported ripping Realaudio/video were discontinued due to legal difficulties, and the only way to do it is with an archived trial and a crack
Don't ask, just DON'T ASK!