First you need to download the stream. There's a program called hidownload. Search it on google, don't know .. there are also tutorials online, where is written down how to get the right link to download it ..
Then you must find a way to convert the downloaded file to mp3 ;D
But I can tell you whats a good program to rip your audio cds to PC ;>
Check it out. Its the best program I know, for that ;D
Use the LAME codec for your mp3s