Have you tried the Mic in?
I have a dedicated DV converter. Miglia, for example, make little Firewire boxes that accept analogue input and convert them to a digital format. I use a Formac Studio (but I wouldn't recommend it). You then need a cable that goes from headphone jack to composite audio (red and white jacks for left and right audio channels). You put those composite jacks into the converter, and the converter connects to the computer by Firewire.