Over in the Potato forum, there is a thread on Propagating Sweet Potatoes that would probably be very helpful to you.
http://www.tomatoville.com/showthread.php?t=13550
I've purchased sweet potato slips for the past two years, but will try to grow my own slips next year, from this years harvest!
As for the OT, I had some Hawaiian/Okinawan Sweet Potatoes while in Hawaii earlier this year, and I could not find a supplier of slips for them. So I will be in search of an asian store or some source for tubers to grow slips for next year. I loved the color and want to grow my own!!