Since the American release of the film Adaptation, author and journalist Susan Orlean has been receiving emails from people who are convinced she does not really exist. "I don't think it would take much (time or money, these days) to cook up a phony website, a phony book, including a phony ISBN number, etc," writes Nathan. "So tell me: are you fer real?"

Orlean is for real. The trouble is that since Adaptation - which has been nominated for four Oscars, won two Golden Globes and the Bafta for best adapted screenplay - came out, she has developed something of a dual personality, one of them fictional.

The personae have a lot in common. In the film, and in real life, she is a staff writer for the New Yorker who went to Florida to write a story about a man, John la Roche, so driven by his love of orchids that he ended up being arrested for his part in stealing them. Both expanded the story into a book, The Orchid Thief, while their first marriages failed. The book, which interweaves the issues of passion and obsession with La Roche's story, was then optioned by a film studio to be adapted by screenwriter Charles Kaufman. But there the similarities end.

For towards the end of the film, the plot takes a peculiar twist. Orlean's celluloid character, played by Meryl Streep (turn the page now if you like surprises), has an affair with La Roche, becomes hooked on drugs and then tries to shoot Kaufman. The real Orlean went back to her day job on the New Yorker and started work on a book about a woman in New Jersey who keeps tigers.

Quite how people could get the small, engaging 47-year-old dog-lover of reality confused with her unhinged cousin of the big screen is difficult to imagine. But they do. When she did readings in the past, she says: "People would ask, how can I get an article published in the New Yorker, how do you use your subjects, things like that." Now they want to know about drugs, guns and whether she really has sex with people she interviews.

"I don't resent it because the curiosity is understandable. But sometimes, particularly questions about my marriage, I find uncomfortable. The stuff about drugs and guns is so patently absurd that it doesn't bother me."

Orlean is not claiming victimhood. Before she agreed to the project, a friend who is a screenwriter warned her: "You can't even imagine what the impact of movies are on the general consciousness. It's a geometric increase of impact and I'm not sure you want to do it." And Streep told her when they first met at a screening in New York: "This is going to change your life a lot more than it's going to change mine."

Orlean got a taste of what Streep meant when she walked the red carpet at the Golden Globes to the accompaniment of flashing cameras. Told where to stand and when to smile, she found the experience both fascinating and "infantilising". "You're both the object of immense admiration and you feel humiliated," she says. "Meryl Streep is used to that. But she doesn't play Meryl Streep qua Meryl Streep, she plays somebody else. She's never been the subject of a film."

Orlean says she is on a journey that she is determined to enjoy, even if the destination is unclear. "You know, I'm doing this as an adventure. I'm doing it as the world's most interesting amusement park ride. What's it like to have your being presented as a character in a movie?"

She nearly didn't start the ride at all. "When I first read the screenplay, I asked them to change the name." Kaufman and director, Spike Jonze, pleaded with her to keep it in as it was essential to the postmodern nature of the film, where the plot feeds off real-life stories. "They really wanted everybody's real name. That was when I started to realise they were trying to make a really different kind of movie," she says. "Also, having my book credited to a different author would be very peculiar."

She drew the line at the inclusion of her parents, who did not make it past a rough draft. "I'm part of the ironic generation and being a writer I have chosen to be somewhat public. But even though my parents were easy-going about it, I thought it might be a little too much. In the draft they were going to show my mother as an alcoholic. She doesn't drink at all."

But otherwise she became excited by the process. "I felt like I wrote my book and someone was borrowing it. Like someone borrowing your dress and wearing it with completely different accessories and shoes, and when you get it back, it's still your dress. I just thought: it's their project now."

In fact, she says, her clothes were considered: "They went through my wardrobe for inspiration and they went in another direction. I sent them my notebooks from the story and the book and they came to my apartment and interviewed me at length on video and then showed it to Meryl Streep."

Streep won a Golden Globe for best supporting actress for her performance and is up for the same award at the Oscars. Orlean was delighted by the way Streep approached the role. "But she didn't choose to study me. It was not an impersonation. She was a little older and a little more conservative. And that made it comfortable for me. There was that character and then there was me."

There were occasional attacks of angst. "There were moments before the movie came out when I would have flickers of paranoia. I'd think 'Is this embarrassing? Is it a massive joke on me? Is it going to make it impossible to work properly again?'"

So aware is she of the peculiarity of fame, in all its glorious dysfunction, that at times it almost seems as though she's talking about it all happening to someone else. "People have congratulated me about the movie, but I had nothing to do with the movie. People I hadn't heard from in 30 years would get in touch. People want things from you. Chefs want to come and say hello and you think, 'Why? I couldn't get a table here a few weeks ago.' It's startling."

But for the most part she has been more intrigued than intimidated by the experience, fully aware that, like the film that made her alter-ego famous, it may yet contain some unpredictable twists that are beyond her control. "I don't know if the full impact is hitting me yet, but I'm definitely feeling like it's too late to take it back. You become something in some minds and you have nothing to do with it."