Ishmael Beah doesn't realize it, but he's about to become a rock star. Well, the literary-humanitarian equivalent of a rock star. (I'll eat my hat if he does not meet Bono in the next 12 months.) Beah, 26, slight and handsome with a ready but wary smile, has written a memoir, and it's a doozy. Separated from his parents at 12 when rebel soldiers attacked his Sierra Leonean village, by 13 he was a child soldier and a drug addict. By 19 he was living in the U.S., at Oberlin College, in Ohio. In February he's starting on a book tour.