Last July, when Poppy Montgomery got the nod to audition as Marilyn Monroe for Blonde, a CBS miniseries airing May 13 and 16, she decided to take a gamble. "I didn't do the breathless Marilyn voice," says the Australian-born actress. Nor did she opt for the platinum-blonde wig or skintight gown. "I came in with a ponytail, a white T-shirt and jeans." In short, she was Norma Jean Baker, the sexually abused foster child turned pinup girl and fashion model before she became Hollywood's all-time favorite sex goddess.

Her strategy paid off. Montgomery's audition scene—a fantasy sequence in which a pregnant Marilyn confronts her mentally ill mother, Gladys—convinced producers of the series, based on Joyce Carol Oates's 2000 novel, that out of the 100 actresses vying for the part, they had found the one who could capture Monroe's pain as well as her pluses.

"A lot of them were frightened by the dark and tortured story," says casting director Wendy Kurtzman, and said they needed more time to prepare. Montgomery, 25, a veteran of two short-lived U.S. TV series (Relativity and The Beat), was given just a couple of days' notice of the audition. Fortunately, says Kurtzman, "Poppy knew a lot about Marilyn, and she just jumped in."

In fact, growing up in Sydney, Montgomery had filled her bedroom with Monroebilia, including books, posters and movie videos (her favorite: 1961's The Misfits). "I don't know what triggered it," she says of her Marilyn mania. "But what I gleaned from biographies was that she gravitated to the underdog. If someone was at a party and no one was talking to that person, she would. I think she had a sense that she didn't fit in either."

Montgomery could empathize. Her parents, Phil Donahue, 58, a restaurateur, and his wife, Nicola, 53, a market research executive, named Poppy Petal and her four sisters—Rosie Thorne, now 24, Lily Belle, 17, Daisy Yellow, 15, and Marigold Sun, 12—after flower fairies in a children's book. (Their brother, Jethro Tull, 34, was named for their parents' favorite rock musician.) At school, other kids would taunt Montgomery as "Floppy Poppy" and "Poopy Poppy." It didn't help, she says, that "I had freckles and red hair and was chubby."

Things weren't much better at home. When she was 12, her parents divorced. Though the split was amicable and both adults (since remarried) remain friends, "it was horrible" after her mom moved out, says Montgomery. "You realize you will never do things as a family again."

At 14, she dropped out of school and went to work waitressing for her dad. "I was terrible," she says. After a few months, "my father called me up and fired me." She had better luck landing roles in community theater productions of Shakespeare. "She always wanted to be an actress," says sister Rosie, now a Hollywood makeup artist.

And so, at 18, after a fling with a boyfriend in Florida fizzled, Montgomery got both parents' blessing to pursue a Hollywood career. Adopting her mother's maiden name, she made the audition rounds, first landing a fast-food commercial. She turned a corner in 1995, earning guest shots on shows such as Party of Five and NYPD Blue.

A year later Montgomery was cast as Jennifer Lukens on Relativity, where she became fast friends with costar Jane Adams (Wonder Boys). And it was Adams who convinced her she could actually play Marilyn. "I was so scared," says Montgomery. "But Jane said I was born to do it."

Off-camera, Montgomery was anything but the insecure Marilyn. "She could really talk trash—funny risqué jokes," recalls Griffin Dunne, who plays Monroe's third husband, playwright Arthur Miller. Montgomery agrees: "I have a mouth on me. Nothing shocks me. Guys feel like they can guy-talk around me."

If there is no guy in her life now, it's because "I am focused on my work," says Montgomery, who lives alone in a one-bedroom garden apartment in West L.A. Waiting for the next project to come along, she says, "I will stay at home and hang out with my friends and play Scategories or Cranium. I don't plumb the dark side. I save that for work." Although, she adds a bit wistfully, "I could have done Marilyn forever."

Frank Swertlow in Los Angeles