DELAYED: Previews of Madonna's London stage debut, in the David Williamson comedy "Up for Grabs," have been postponed three days because of technical difficulties, the producers told Reuters on Monday. Three previews have been canceled (they were to begin May 9), said a spokeswoman, but opening night will remain May 23. "Everybody in the cast has been very accommodating," the rep told Reuters, obviously referring to the star, 43 . . . BOUGHT: Oprah Winfrey, 48, and her former personal trainer, Bob Greene, age unreported, are purchasing seven shoreline lots in Hawaii to build several homes, including one on a 102-acre lot for the talk-show queen, Winfrey's spokesman told the Associated Press. The two reportedly intend to put conservation first and keep the development low key . . . REDUCED: HBO's hit series "Sex and the City" has been cut to eight episodes from its originally slated 13 as a result of star Sarah Jessica Parker's unexpected pregnancy, says The Hollywood Reporter. (HBO, like PEOPLE, is part of AOL Time Warner.) The series' fifth season is scheduled to resume production in New York May 6 and will launch in early July, an HBO rep told the Reporter . . . ADOPTED: Former President Bill Clinton, who lost his beloved chocolate Labrador Buddy in January, is about to welcome a new puppy to his house in Chappaqua, N.Y., reports the New York Post. The new dog is 3 1/2 months old, is another chocolate Lab, was sired by Buddy's nephew and weighs (as of this weekend) 25 pounds, says the paper. For now he's being called B.B. -- for Bill's Boy-- though, reportedly, Clinton, 55, does have a permanent name picked out for him. Buddy II?