BOY, OH BOY. WHEN HILARY SWANK ASCENDED THE STAGE IN A flowing Randolph Duke gown to collect her Best Actress Oscar, many gasped: The star of the gender-bending drama Boys Don’t Cry was a knockout. For her riveting portrayal of Brandon Teena, the Nebraska youth who was born female but lived as a male, Swank, 25, submitted herself to a barber and strapped her breasts down under baggy flannel shirts. The utterly convincing result? “When some people met her on the set, they thought she was just another guy in the room,” says costar Brendan Sexton III, whose ex-con character buys into the deception. “Sometimes I even thought of her as a boy. Hilary has a strong jaw and strong cheekbones, very good things to have as either a woman or a man.” Swank, a former competitive swimmer and gymnast from Bellingham, Wash., was also up for some serious male bonding. “She is definitely tough,” says Sexton. “We had to wrestle in the movie, and she was feisty.” The 57″ Swank has had to be. At 16, she moved to L.A. to pursue acting, accompanied by her mother, Judy, 51, an executive secretary, then separated from Swank’s father, Stephen, 52, a National Guardsman. For a time the two were so impoverished that they lived out of their Oldsmobile Delta ’88. Eventually, Swank landed parts in 1992’s Buffy the Vampire Slayer and 1994’s The Next Karate Kid. She had no trouble snaring a starring role with actor Chad Lowe. At a 1992 party, “I saw her and saw our future in her eyes,” says Lowe, 32, who married Swank five years later. “She had the most beautiful eyes I’d ever seen. They speak volumes about her character.” Aaron Spelling thought so too and gave Swank a recurring role on the 1997-98 season of Beverly Hills, 90210. “She is a real presence,” he says. “Understated but gorgeous.” For his part, Brendan Sexton can still recall the moment he first saw Swank in a dress. “It was at a party near the end of the movie’s shoot,” he says. “I was blown away. She was so beautiful.” And definitely not a boy.