I think you can use the recorder that comes with Windows and just do an audio recording. You can record from the stream as output from the sound card. I haven’t done this recently but open the recorder (Start, Programs, Accessories, Entertainment or Multimedia, depending on what version of Windows). Try this out in advance. Find a web site that has RealAudio (ideally the station you want to record from) and see if it will work. The recorder might only record off the microphone, but I think it will record from any sound card output.
I think there are tools around that allow you to capture the digital audio stream and save a copy, but I’ve not used any so I don’t have a recommendation.
The difference is that in the first method, you are capturing the analog audio and recording it to digital, whereas in the second case you are making a perfect digital copy, like ripping a CD.