This video (slightly out of date as skype didn not go away) shows how to adjust your callers volume. 

http://www.schoolofpodcasting.com/callburner  (PC)

If you're on a Mac check out Call Recorder from ecamm http://www.schoolofpodcasting.com/callrecorder

This one does similar but shows how to use a portable recorder (I usually use both)

http://youtu.be/xYAzrplpVSs

Here is a great video from my friend Ray Ortega about how to setup a mix minus.

http://youtu.be/au47Ferbxfc

Please let me know if you need more help.