A sandy stretch of Miami's South Beach, tricked out like a whirling carnival for coeds, is where Justin Guarini and Kelly Clarkson ''meet'' for the first time. They lock eyes and shimmy playfully toward one another while lip-synching a catchy pop song called ''Bounce.'' Though it's late January, this scene in ''From Justin to Kelly'' has all the joie de vivre of spring break, minus a few key elements: Where are the cussing frat boys? The skulking crew from ''Girls Gone Wild''? Why are the extras tossing Frisbees instead of their cookies? Clarkson rhapsodizes during a temporary gyration break, ''There's been nothing like this since 'Grease!'''
Unfortunately, there was something after ''Grease'': It was called ''Grease 2.'' And watching the filming of the quickie production ''From Justin to Kelly'' (Fox, the acronym-happy studio that brought you ''X2'' and the upcoming ''LXG,'' is internally calling it ''J2K'') engages the viewer in a perpetual struggle of nice versus nasty. When Clarkson sings, you can imagine a mini-Paula Abdul hovering above her cheering ''This is the 'Matrix' of musicals!'' But when her costar tries being a human beat box, you can almost hear Simon Cowell hiss, ''This is a bloody train wreck.'' Which is fine by Guarini. ''[People] will come in with misconceptions,'' says ''American Idol'''s springy-haired 24-year-old runner-up. ''It's going to be a strong movie.''
Fact is, the real Paula and Simon are nowhere to be found -- and when original ''AI'' competitors RJ Helton and Christina Christian dropped by the set, it was for visits, not cameos. ''Simon isn't going to show up and push anybody into the pool,'' assures Kim Fuller, the film's screenwriter and brother of ''J2K'' and ''AI'' exec producer Simon Fuller. ''[The movie] has nothing to do with the show.'' But will fans pony up $10 to see the goods they watched on free TV way back when, pre-Ruuuuuben? ''It was risky,'' admits Kim, who also penned ''Spice World'' (which made a bland $29 million at the U.S. box office). ''If people's expectations are going to be greater than 'it's just a couple of kids making a movie and having fun,' they'll be disappointed. It's not 'One Flew Over the Cuckoo's Nest.'''
The ever-perky Clarkson is more optimistic: ''This is 'Chicago' for a younger audience.'' That comparison isn't exactly music to director Robert Iscove's ears. Bleary-eyed from the day's shoot, Iscove (''She's All That''), 55, is exhausted from trying to make the $12 million, 10-song film in just over 30 days. Iscove is best known for 1997's Emmy-winning ''Rodgers & Hammerstein's Cinderella,'' starring Brandy and Whitney Houston -- and tapping Rob Marshall as his choreographer. Yes, the same Rob Marshall who later directed ''Chicago.'' ''For four years Harvey [Weinstein] told me [''Chicago''] was going to be my Oscar movie,'' contends Iscove. (Weinstein's rep says that Iscove was involved with the project but wasn't guaranteed the directing spot.) Now he's under so much pressure to wrap ''J2K'' that he's had to shoot some scenes without rehearsal. When asked what his next project is, Iscove jokes, ''The sanitarium.''
As for 21-year-old Clarkson, she didn't know it while shooting, but she was about to have a lot to be ''Thankful'' for. According to Nielsen SoundScan, her album, which she hustled to finish in late February and March for its April 15 release date, debuted atop the Billboard chart and made good on the promise of her single ''A Moment Like This,'' selling over 800,000 copies (the 1.3 million figure that Clive Davis announced on ''AI'' referred to shipping, not sales). Guarini's self-titled effort drops June 10, ten days before ''J2K'' hits the theaters. So as not to divide ''AI'' audience dollars -- since singles by Ruben Studdard and Clay Aiken will also hit stores in early June -- 19 Entertainment (which created the ''AI'' juggernaut and reps both Clarkson and Guarini) and Fox say they scrapped plans for a ''J2K'' soundtrack. Which means that Justin and Co.'s hip-hop cover of KC and the Sunshine Band will only be in theaters.
It's nearly midnight in Miami as Kelly, sporting platform frankensandals and a skirt that looks stitched out of magicians' handkerchiefs, does her umpteenth amble down a palm-tree-lined promenade, mouthing the words to the ballad ''Anytime.'' In ''Grease'' terms, this is Clarkson's ''Hopelessly Devoted to You'' scene. In viewers' terms, little Paula's cooing ''She's just like Olivia Newton-John!'' With Simon shooting back, ''Sure, in 'Xanadu!'''
''I was the most skeptical about how things were going to turn out,'' insists Clarkson. ''But I think it's going to be a shocker. It's going to take everyone by surprise.'' And at least on this night, nobody's about to argue with Miss Independent.