HILARY DUFF just can't keep a personal diary.

"I've tried before and it's lasted about four days," says the 16-year-old singer-actress. "I do keep one on my Web site so all my fans can see what's going on with me, but you know what? When you're busy, it's really hard!"

Duff's most recent online entry is dated May 24. It was datelined Toronto, where Duff was filming the romantic comedy "The Perfect Man," in which she plays matchmaker for mom Heather Locklear.

Friday marks the nationwide opening of "A Cinderella Story," a contemporary twist on the classic fairy tale, featuring Duff as a high school girl living at the mercy of a self-obsessed stepmother and two nasty stepsisters. (See capsule film review on Page 49.) When she meets a potential Prince Charming on the Internet, complications, confusion and happily-ever-afters ensue. The film's soundtrack features four new Duff songs, including a duet with sister Haylie on the Go-Go's "Our Lips Are Sealed."

On Tuesday, Duff kicks off a 33-city concert tour that brings her (and Haylie) to the Patriot Center Thursday. In August she'll complete her as-yet untitled sophomore album for release Sept. 28 -- her 17th birthday. Duff's coming-out album, "Metamorphosis," went triple platinum, outselling Britney Spears's and Madonna's last albums combined. And October sees the release of another film, "Raise Your Voice."

Maybe it's a good thing she doesn't keep a personal diary. Who'd believe such fantasies?

"You know what? I feel lucky, I really do," says Duff, calling from Los Angeles recently during one last bit of rest and recreation. "Everything is so crazy for me, and so surreal -- I feel like such a normal girl in this crazy whirlwind world. Sometimes I do feel like it's a fantasy and a fairy tale."

Four years ago, it felt more like a bad dream about to be deferred by a girl from Texas who'd been an aspiring ballerina at 6, started doing print ads and television commercials at 8, and moved to Los Angeles at 10 with her mother, Susan, and sister Haylie, then 12. Father Bob stayed in Houston, where he owned a number of convenience stores, while the Duff sisters studied acting, auditioned like crazy, and got rejected early and often before landing a few small roles.

"My mom and dad are amazing," Hilary says. "My mom works her butt off every single day for me, and I'm sure she'd rather be with my dad in Texas and stuff -- they're just so supportive in everything that we want to do."

For instance, Duff says, "My sister and I must have gone on 100 auditions without a callback, and the minute my mother saw us feel like we'd been rejected or this is over, she'd say, 'I don't want to see you guys being upset about this because you weren't right for it.' She would never let us feel like it was our fault, and that really made us handle it well and everything."

Hilary eventually got bit parts on "Chicago Hope," and in 1998's "Casper Meets Wendy," the direct-to-video sequel to "Casper." Then there was little progress over the next two years. And when Hilary landed a role in the pilot of an NBC sitcom, "Daddio," only to be dropped from the cast before its inglorious three-episode run, she was ready to quit.

There was one more call. Duff told her mom she wasn't going up for the role.

"But they sent a plane ticket to come back and audition for it, and I said okay, though I didn't really care about the audition. I went in and I guess I did a good job."

Indeed. The call had come from Disney, and at 12 Duff won the title role in "Lizzie McGuire," a charming and innovative series about life during the awkward middle school years. Much more upbeat than "My So-Called Life," the cult '90s series about the trials and tribulations of a young girl, "Lizzie McGuire" mixed live action, stills, home movies and animation. Perky, polite, vulnerable and in no great hurry to grow up, Lizzie had an animated alter ego to express her innermost thoughts.

Parents liked the show, but more importantly, kids identified with Lizzie's growing pains: "Lizzie McGuire" was the Disney Channel's highest-rated show after its debut in 2001, with 2 million viewers per episode. Most were tweens, 8- to 14-year-olds, a newly defined, highly desired demographic. There are some 25 million of them with an estimated buying and influencing power (money spent directly and money they get their parents to spend) of $500 billion a year.

And Hilary, with her sweet smile and golden blond hair, suddenly became the "tween queen," with a show that was getting 375,000 e-mails a week.

The funny thing is that while Duff is a relative newcomer to making records, it was music, and sister Haylie, that facilitated the acting career that established her tween kingdom, which also includes a Target-carried Stuff by Hilary Duff clothing and merchandise line.

As Hilary tells it, "early on I had a speech impediment -- I couldn't say my R's. I went to this private school, and they had the biggest problem with it. My mom was, 'She's in the first grade, it's okay, it'll go away, she just needs time,' but they wanted to put me in all these special programs. My mom had heard that if you take singing lessons, it helps a lot, so she thought it would be something that was fun for me and might correct the problem.

"And within a month of going into singing classes, the problem went away, and then I just wanted to keep doing it because I had so much fun. It really opened me up, because I used to be a really shy child, hiding behind my mom's skirts and stuff. But this was something I really loved and felt comfortable with, and I started being able to sing in front of people. But it was always the acting that was the first thing I wanted to do . . . until a couple of years ago."

And that came about through Haylie.

"Our parents were supportive of whatever my sister and I wanted to do, whether it was soccer or ballet or singing," Hilary explains. "When my sister wanted to be an actress, I was, that's such a stupid idea because I was all into sports, this, that and the other. But when she'd come home and tell me all this stuff she learned in acting class, I'd think, 'Oh, my god, that sounds like fun,' and so I started doing it. It kind of pulls you in if you love it, which I do."

In her two years on the show, Lizzie McGuire never sang, though Hilary did, making her debut with "I Can't Wait" on the series' platinum soundtrack album. She didn't have to wait long: "The Lizzie McGuire Movie," in which Lizzie graduates from middle school and goes to Italy on a class trip, found a way for her to sing: seemed she was a dead ringer for the distaff half of a popular Italian pop duo, gone missing on the eve of a globally televised awards show -- Lizzie McGuire to the rescue!

"Metamorphosis" proved the musical equivalent of Lizzie McGuire's coming-of-age, a collection of bright, accessible and, to everyone's relief, age-appropriate songs. The first single, the Matrix-written and -produced "So Yesterday" went to No. 1. The album soon followed.

In 2003's "Lizzie McGuire Movie," Duff left junior high. Now, in "A Cinderella Story," she's graduating high school, hoping to go to Princeton. This extreme fast track is amusing, given that Duff has never attended a day of middle or high school, instead being home-tutored or tutored on various sets, four hours a day as required by law.

"I get asked all the time, 'Do you feel like you're missing out?' I don't know anything else, so how do I know if I'm missing out?" she wonders. "I love my life and I get to travel all around the world. I think that normal kids get stuff that I don't get, and I get stuff that they don't get, and it's just a trade-off."

Plus, she adds, "I think that high school is so cruel these days and kids deal with so much drama."

Though Duff missed the drama in high school, she's certainly finding it these days in the nation's tabloids. There are the widely reported tiffs with Avril Lavigne and Lindsay Lohan (the former over a perceived slight, which Duff apologized for, the latter over mutual rascal/boyfriend Aaron Carter) and, more recently, rumors of romance with 25-year-old Joel Madden, lead singer of Good Charlotte. People magazine reported spotting the two "at restaurants and parties together in Toronto. . . . A source says that the two arrived separately at the MuchMusic Video Awards but were soon seen kissing in the VIP lounge. Reps for Duff and Madden say that they are 'just friends.' "

Duff, emphasizing that career trumps romance for now, agrees. "We hung out! [Joel and twin brother Benji] are just really nice guys and I really love their music. I totally respect them and I think they're cool."

"Here's the thing about that," she says of tabloids and celebrity culture. "Everybody, no matter how much they think it's disgusting or they don't want to read it or buy it, they do. I used to read that stuff all the time! I would read stuff about Britney Spears and I would go, "My god, is that true? I can't believe it because I'm such a huge fan of hers!'

"And now I know that it's just garbage, it's not true. I read stuff about myself all the time . . . and it hurts your feelings. I never had to deal with this in high school, but I deal with it with millions and millions of people reading it and that's really hard sometimes."

On a happier note, Duff is Seventeen's cover girl this month, sporting a demure, dove-gray jacket over a white top. It's a good look for a role model, which, unlike some of her peers, Duff doesn't seem to have a problem being.

"I think that I'm pretty straightforward, and I'm an honest person and if people look up to that because I'm just being myself, then that's cool," she says. "I don't necessarily feel like I have to break away or get out of this type of genre that people have put me in. I do think that I'm growing and my music, especially on this second album that's coming out, is more mature, but not so mature that it's beyond that younger audience, because I do know that I have that younger audience. Same with the movie parts that I take."

HILARY DUFF -- Appearing Thursday at the Patriot Center. * To hear a free Sound Bite from Hilary Duff, call Post-Haste at 301-313-2200 and press 8121. (Prince William residents, call 703-690-4110.)

"Everything is so crazy for me, and so surreal -- I feel like such a normal girl in this crazy whirlwind world," says singer-actress Hilary Duff, 16.