As a general rule with any fruit bearer, the seedlings that sprout from the fruit may not be true to type. This is worst in apples, but less so with some other fruit. Your best chance of getting something that bears true to type is with something self-fertile. Since grapes are self polunating, your chances of getting something good are a little better.
That being said, I've propagated all of my grapes from cuttings, which guarranties they'll be true to type. What I would suggest is try saving one or two and see what happens in a year or two. If however, you really want a high quality vineyard quickly, I'd make cutting off of all of this year's growth, and plant those back in the ground.
Cuttings are extremely easy to
root. Just cut your vines into 15-18" sections, and dip the end closest to the ground in rooting hormone. You can find hormone in the garden section of Home Depot. Do this in the fall after they've lost their leaves, planting the sticks in a spot where they'll stay moist over the winter. I use 15" sections of plastic drain pipe. They will sprout the following spring.
