Hi Susie,
I don't know much about them and I don't know which kind of potato vine you have but I think you should wait a while regardless. You could start them early in pots to move outside later, but I would wait until late winter/early spring. They don't grow very fast until it gets warm but when it does they really take off and you won't have gained much by starting really early.
I left a pot of the invasive kind here (Dioscorea bulbifera) un-watered in an unheated and uncooled greenhouse for two years before dumping the soil out of the pot. I'm now fighting to eradicate them, so if that is what you have there is not much you can do that will hurt them. Other types are not hardy. If your friend is in your zone and hers come back every year that may be what you have.
