How to record a song that playing on the internet in audacity 1.3 beta on the same computer?

Like if there is a song on youtube playing, how do i record it into audacity, its the newest version, so i dont know.How to record a song that playing on the internet in audacity 1.3 beta on the same computer?
Same way as with the 1.2 version..

Select 'stereo mix' or 'what you hear' from the recording input selection box.How to record a song that playing on the internet in audacity 1.3 beta on the same computer?
it is "stereo mix" i tried each of those sugestions under microphone settings and found it was stereo mix