Last week I published a diagram of one way to record Skype calls. This week I’ve got a somewhat different version that eliminates the need for an external mixer.
Assuming your recorder can’t handle a mic-level input on one channel and a line-level source on the other, you’ll need the attenuator shown between the line-level out of the computer and the mic-livel input of the recorder. If you have independent input-level controls on your recorder, a 40dB attenuator ought to be good enough. If you can’t control the levels independently, you may have to experiment with the ammount of attenuation, using more attenuation if your mic is dynamic (to match its low levels) or less attenuation to match higher-level condenser mics. You don’t need to match the levels exactly, since the whole idea of recording on separate tracks is that you can “fix it in the mix.” Just watch out: You could spend as much for an attenuator as you would for a mixer!