Are these hardy at all? How do you over-winter them?

No - they are not hardy but here they just go dormant and come back year after year.
I know in Holland they are sold as a house plant.

I found this information:
http://gardenofeaden.blogspot....

Mine are overwintered dry in their pots in the basement. They're listed hardy for Z 8 and 9.

Thanks both of you.

I'm growing mine in a large container per jmorth's instructions and they have flower buds already! I'm fascinated by how the leaves have tendrils on the ends.

I'll just bring the container into the garage over winter. Next year I will try planting one tuber in the ground and see if I can over-winter it with heavy mulch protection.

I know it is a very cool climber!