That perennial Brit-in-New-York Tina Brown, who has followed the public life of Princess Diana ever since she emerged onto the scene in 1980, has been signed to write the book she seems born to do: a study of the late princess's impact on the media, the world at large and the often-embattled Royal Family. None other than Phyllis Grann signed it for Doubleday, and will edit it for the house; she got North American, first serial and audio rights from agent Ed Victor, who himself once made a transatlantic transition in the other direction. The book doesn't yet have a title, but they're pushing to get it out by early 2007, shortly before the 10th anniversary of Di's death in a car crash in Paris. Brown, now a TV star in her own right, covered both Di's wedding and funeral, and will be on hand to talk about Prince Charles's upcoming wedding on The Today Show next month.