Tonight Yarn's show in Nashville is being streamed live at 8pm eastern time The link to the streaming site is on Yarn's web site. Hope you all check it out.
Audacity is a free download and makes it really easy.
It will export as most any type of file, but I think the best you're gonna get is a 128k stream, so it might as well be mp3. Depending on your settings and what program you record with, it may record any sound your computer makes, so shut down anything that pings or beeps and don't plug/unplug any usb devices while you record.
By the way, I've been after them (as one of the few worthwhile music print magazines left) to profile the band for some time now. Someone else might try e-mailing their managing editor Evan Schlansky at eschlansky@americansongwriter.com