Some 600 members of the Shinnecock Nation, notes Ariel Levy in The New Yorker, live near tony Southampton, L.I. But with an annual median household income of about $14,000, theirs is a life far different from that of their affluent neighbors. With their plans to open a casino in Southampton, this chasm has widened. Southampton residents are fearful that cars, crowds, and garishness will ruin their rustic surroundings. The Shinnecocks, who became a federally recognized tribe this fall after 32 years of effort, are equally determined to cash in on their new status.