SOON AFTER DROPPING OUT of her New York public high school, Jacki Simmons started writing her first novel, typing on a borrowed computer during half-hour lunch breaks at a day care center and spare moments at work and home. Now, the Harlem 19-year-old's book, "Stripped," has been published - and Simmons is back in school a few credits shy of her diploma. "I never actually expected it. I never thought it was going to happen," said Simmons, who still lives at home with her family and pays her bills with a day job at Babies "R" Us in Yonkers. "It was a shock." Simmons didn't have an agent, a degree or much hope this spring when she mailed her manuscript to Melodrama Publishing, a Bellport, L.I., company she found on the Internet. The publisher's urban fiction and "street lit" frequently top the Essence Best Sellers list. But two weeks later, Melodrama bought her book for an undisclosed sum. It was published in November, and Simmons even went on a book tour to Philadelphia, Baltimore and New Jersey. "Stripped," a risque coming-of-age story about a college student who turns to stripping after losing her wealthy fiancé, is being sold at independent stores such as Hue-Man Bookstore in Harlem and Melodrama Books and Things in Far Rockaway, Queens, as well as by vendors who hawk it on the street. It sells for $15.00 a copy on Amazon.com. At the urging of her mother, Wanda, Simmons will get her high school diploma in January from Independence High School on Manhattan's West Side, a "transfer school" designed to meet the needs of students who dropped out of other schools. "I think she's going to be a famous author," said Principal Ron Smolkin. "We're all sort of in shock that we have a young person who has published a novel." Simmons, a pseudonym the author uses to avoid attention in her neighborhood, began writing stories as a child in the Harlem apartment she shared with her parents and four brothers. English classes were an oasis for her at the Academy of Environmental Science High School in East Harlem, the only courses she never failed or cut. "Constructive criticism is a must, and they gave it," she said of her teachers there. "It was the only reason that I'd go to school." But it wasn't reason enough. She started cutting classes in the ninth grade and, by the 11th, was barely going to school at all. Her first long-term relationship was ending. She was bored at school and no longer saw the point in going to overcrowded classes. Books were in short supply and no amount of needling from the attendance teacher could change her mind. Simmons dropped out completely her senior year and began volunteering at a Head Start program with her mom. That's where "Stripped" began taking shape. As Simmons wrote one day, a co-worker peered over her shoulder and read from the computer screen. "She said, 'Girl, this is good! You should get this published,' " she remembered. "And I said, 'You think so?' "