Melanie Lynskey and Kate Winslet giggle as they walk, arms clasped. They are momentarily lost in a world of inside jokes and fond memories. Or maybe they're simply overcome by the excitement of it all. When they describe the glamorous hotel rooms and limousine rides they've had the past few days, they gasp and squeal.

It's understandable: Teenagers don't usually get this kind of treatment. Lynskey, prim-looking despite her thick tights and combat boots, and Winslet, svelte and blonde in a snug sweater, are basking in their new roles as movie stars - well, almost movie stars. The unknown duo, 17 and 19 respectively, opened last week in "Heavenly Creatures," about New Zealand's infamous Parker-Hulme murder.

Like the girls accused and convicted in the 1954 murder trial, Lynskey and Winslet share a bond that excludes everyone outside their circle of two. Both vegetarians, they order identical salads and talk with the relaxed, easy manner reserved for best friends. But there is one major difference between the young actresses at the table and the characters they portray. Somewhere along the line, the friendship between Pauline Parker and Juliet Hulme went terribly wrong. They did, after all, carry out a brutal and carefully planned matricide. And when they were finally released from prison, it was on one condition: that they never see each other again. (Juliet was discovered recently writing mystery novels in Scotland under a pen name: She happens to be the best-selling author Anne Perry. Pauline apparently lives quietly in New Zealand.)

"Neither of the girls had ever had a close friend before,"  says the director, Peter Jackson ("Dead Alive"), explaining why Pauline and Juliet put such fervid energy into preserving their friendship. The girls thought Pauline's mother, Honora Parker, threatened their relationship. "And in the case of Juliet, she'd never had a close relationship with her parents. The murder in a way is secondary. It still would have been a great story if it didn't have the murder."

But, of course, it did have the murder, and above all, Jackson wanted to avoid the sensationalism previous tellings of the story had favored. Research for the script he wrote with Fran Walsh included poring through court documents and newspaper reports that described obsessed lesbian lovers. But the essense of the friendship came alive for Jackson of their classmates from Christchurch, where the girls went to school. "Pauline was this powerhouse - this fiery, intense, silent girl who looked sullen and was quite frightening to many of the girls," says Walsh, who conducted the interviews with classmates. "And Juliet was this very arrogant, stately, snooty English girl who they all were in awe of and quite admired."

Opposites attract, and in Pauline and Juliet's case, the result was explosive. As Jackson shows their friendship develop on the sidelines of gym class (they were both kept out of phys ed for health reasons), their combined imaginations create a spark neither had experienced before. Jackson was set on finding actresses who looked like the real girls. "I was never making a documentary, but I wanted to make it as accurate as it possibly could be," says Jackson. "There are people who remember those girls, remember the house, the school. We had to get those things right - to make it believable."

He found Winslet, a startlingly precise match for the blonde Juliet, in a London audition. She also passed the "intelligence interview" that Jackson insisted on before signing anyone to play the brainy principals. But the right Pauline Parker was harder to find. After an unsuccessful sweep of New Zealand drama schools and troupes, Walsh took a black-and-white photo of Pauline and began combing high schools. With only four weeks left before filming, she discovered Lynskey in a classroom in New Plymouth, New Zealand. Her pale skin, dark hair and still-pudgy figure made her a dead ringer for Pauline. "The teacher pointed out Melanie and said, `She writes great poetry, is incredibly bright and she's really good at drama,' " says Walsh. Lynskey, 15, won the role over 600 actresses, despite the fact her acting experience consisted of school plays and community theater. And although the movie's success was riding on the ability of these girls to convince us they would do anything to keep from being separated, they were never auditioned together.

"I don't really believe in the karmic thing about onscreen chemistry," says Jackson. "Even if you audition them together, you're not going to know. After two weeks they could have hated each other's guts." As it turned out, that was far from the case. Sitting across from her co-star, picking at her salad coyly at the Four Seasons Hotel, Lynskey recalls arriving in Christchurch two years ago. "Kate looked like such a movie star when I saw her in the airport," she says, amused. "She had this leather jacket and jeans and long blond hair. And I felt like such a little . . . I felt terrible."

Then Kate chimes in, shifting her confident British dialect to mimic Lynskey's close-mouthed New Zealand one: "Mel's mother says, `Oh,there was such an amazing chemistry between them, it was so instant.' " At this they break into peals of laughter and agree it was true.To get in the spirit of the parts, they went to the Ilam Homestead, the palatial estate where Hulme grew up. They ran through the lush gardens where much of the movie's onscreen friendship blooms, and they began to understand the transporting qualities of the idyllic place. As the characters' friendship strengthens, the love-starved girls start showing affection for each other physically - holding hands, hugging or even kissing.

By the time Lynskey and Winslet undressed for the camera - for a scene in which Pauline and Juliet fantasize how their favorite movie stars would make love - the two hardly flinched. After all, they'd already "had a lot of baths together," as Winslet points out. The luxurious on-screen baths, she says, were actually exercises in contortion. "We look so comfortable in this bath, and really, the water's freezing and my toe's up Mel's bum."

"Yes," Lynskey mocks, as if summoning a misty-eyed memory. "There were those beautiful naked moments together." So when it came to " that kissing stuff," according to Winslet, they were ready. "It was kind of fun, like we were playing a game," she says. "We knew it was innocent. It was just so lovely, because we knew that they did love each other insuch a unique way."

Lynskey agrees, but adds: "It was a bit weird to be kissing Kate. I'd never thought about it very much." She looks at her friend. "Sorry," she says. Winslet is not offended, but puts on a grin and a deep lecherous voice, "But it was good." While their off-screen friendship naturally fed into their onscreen bond, the emotionally wrenching scenes - of which there are more than a few - took some work. Especially for Lynskey, who had never had any professional training.

To make herself cry, Lynskey thought of a close friend who had drowned four weeks before the movie began filming. To help her get and stay in character, Jackson never used stand-ins. The actresses worked so well together, he kept them both on the set at all times. Before certain scenes, he'd ask Winslet to go over to Lynskey and in Juliet's voice whisper, "I love you." That little voice haunted Lynskey, she says, and jolted her into character. The toughest scene for everybody, of course, was the murder, which they filmed at the end of the 11-week shoot. Leading up to the scene, the characters rationalize the brutal act they've been planning for weeks.

Juliet, in her grandiose language (in fact, her actual words as recorded by a court psychiatrist) says, "Only the best people fight against all obstacles in the pursuit of happiness." But how did the real-life teenagers cope with the brutal act they were about to commit? Winslet says they never actually did. It was too hard. "If we ever stopped and thought, `Oh, - , this is what they did . . .,' " she trails off. "They took a brick in their hands and theykilled this woman - they smashed her head in. It's so disturbing and frightening, we have to not think about it." We see the girls, hysterical and covered in blood, running at the beginning and end of the movie. To get worked up for the scene, Lynskey and Winslet ran in circles high atop Christchurch in Victoria Park until they were close to hyperventilating.

"The worst thing was we couldn't just go home and say, `Oh well, it's just a story,' " says Lynskey. "You can understand everything leading up to the murder. You can even understand moments before. But actually doing it was the most horrible, horrible thing."

"I really don't know how people just step in out of roles," Kate says, looking back at her sensational debut at 17 as real-life teen murderess Juliet Hulme in Peter Jackson's HEAVENLY CREATURES "I knew that girl," she insists. "I was that girl. I knew her fantasies, her craziness. I remember researching the period through newspaper stories on, what's the word, microfilm, and as I drew near the murder date my heart started pounding like mad and I could barely keep on reading. "And nobody warned me that there's this comedown after a movie," she adds. "I spent days and days just crying, trying to get the whole thing out of me, and I never really did. Juliet Hulme is still in there. I think most of my characters still live in me. I mean, it takes me a month after filming just to come back down to earth."