Answer: Early spring is the time to plant grapes - that's when you'll see them offered in nursery catalogs. You have plenty of time to plan your plot. Grapes require a very deep, well-drained, fertile soil, so start improving the planting site now. As for which varieties are best for your area, your county agricultural extension office can give you that specific information. If there is a nursery on Long Island that specializes in growing fruit stock for your area, check with them. Locally grown stock is best suited to your conditions, and should perform very well. If there isn't such a place, your extension office can make a good suggestion.
Cornell University Extension offeres a very helpful low-cost bulletin called "Home Fruit Planting" that covers the basics of grape culture, including training and pruning (order from this website: http://www.cce.cornell.edu/publications/fruit.html
Q&A Library Searching Tips