The first thing you hear in Crossroads, a film that stars Britney Spears and her belly, is the giggling of young girls. This is appropriate, since young girls are the only ones likely to enjoy this vapid road-trip movie. Their parents are more likely to groan softly at the prospect of having to hear the soundtrack over and over.

Crossroads is Spears' film debut, and to be fair, she exudes more charisma than you might expect, a lot more than fellow pop singer Mandy Moore does in the recent A Walk to Remember. Let's face it: Spears is relentlessly cute, and she has a stage presence, even if she won't give serious young actresses (say, Ghost World's Thora Birch) any competition. That appeal, and the fact that she appears half-dressed quite a bit, make it almost certain this won't be her last film. Whether this is good news, however, remains to be seen.

Spears plays Lucy, a small-town Georgia valedictorian who is labeled, hilariously, a nerd. (I don't know what your high school was like, but at mine, this girl would have been prom queen, homecoming queen, May queen and just about every other kind of queen imaginable. They would have invented titles just to bestow them on her.) As children, she and her best friends Kit (Zo Saldana) and Mimi (Taryn Manning) were inseparable; now, at graduation, they've drifted apart. Kit, the popular one, cares only about planning her wedding; Mimi is pregnant. Lucy has vague plans to work at a hospital, a job set up by her garage-mechanic dad (Dan Aykroyd, shakily dusting off his accent from Driving Miss Daisy).

With a little help from movie magic, the friends reunite, with Kit and Lucy deciding to join Mimi on a road trip to California, where Mimi hopes to try out in one of those realistic talent contests that accepts all entries and presumably leads to fame and riches, even if one happens to be a pregnant, talentless teenager (there's also a convenient karaoke contest along the way, which will help the heroes pay for the requisite broken radiator). Kit wants to see her boyfriend at college, and Lucy hopes to stop in Tucson to see the mother (Kim Cattrall, Sex and the City) who abandoned her. All three will get their moments of hokey melodrama.

Driving is hunky, tattooed Ben (Anson Mount), a friend of Mimi's, who complains a little too much about having to chauffeur attractive, underage girls across the country. The girls think he might be dangerous, but this does not stop Lucy from offering up her belly, and her virginity, once they get to California.

There are all sorts of little in-jokes for Spears fans: Her little sister Jamie Lynn, who looks exactly like Spears, plays Lucy as a child. The girls sing boisterously to the radio and squeal when they hear Bye Bye Bye, sung by Spears' real-life sweetheart, Justin Timberlake.

But non-Spears fans will remain unmoved and may actually bolt for the exits upon hearing the opening lines to I'm Not a Girl, Not Yet a Woman, which Spears performs, sort of, at the end. In the film, Lucy pens the lyrics, and Ben puts them to music. That's the one believable conceit in Crossroads -- the song is so dreadful it makes sense that an inexperienced kid would have written it.