Question
can i start a new grape vine from the root of an existing one?

Answer
Hi Bill,
Thanx for your question.  It is easy to start a grape plant from the root of an existing one.  You may also start grape plants from cuttings at least 8 inches long(not much longer) and rooting in clean glasses of water.  If you are separating roots make sure you have a clump of roots at least the size of a golf ball.  This should allow for enough root material   I hope this is enough information.  If not, please post a follow up.
thx,
Tom