Instead of doing a straight- ahead remake of the popular ' 60s TV show "Bewitched," Nora Ephron came up with an ingenious spin: she's made a movie about other people making a new TV series of "Bewitched." The twist is, the producers unwittingly hire an actual witch to take the role of the nose-wiggling Samantha, the part originally played by Elizabeth Montgomery.

Isabel (Nicole Kidman), the witch in question, has never acted in her life, which is just fine with her leading man, Jack Wyatt (Will Ferrell), a vain, down-on-his-luck movie star who hopes to resurrect his flagging career with the show, and wants all the close-ups. Isabel, on the other hand, is tired of getting anything or anybody she wants with a snap of the fingers. She wants to be needed for herself, without using magic, and she's naive enough to believe Jack's interest in her is genuine.

This pop-Pirandellian concept, written by Ephron with her sister Delia, yields some healthy laughs. The comedy works best on the set of the new show, where Isabel nails the audition with her inspired "in character" improvisations. Once Isabel discovers Jack is using her only to make himself look good, she begins to slip, reverting to her old spell-casting ways. Suddenly Jack's acting takes a decidedly bizarre turn. Adding to the fun is Shirley MacLaine as Iris, an attention-hogging actress cast as Samantha's witchy mom, Endora, who captures the lecherous attentions of Isabel's warlock dad (Michael Caine).

As long as it stays focused on showbiz, "Bewitched" is light, frothy fun. But Ephron ("Sleepless in Seattle," "You've Got Mail") insists on turning "Bewitched" into a love story, and that's when the fun starts to seep out of the movie. That's also when it stops making sense, even on its own nonsensical terms. No matter how many times Isabel's passion for Jack is explained to us, it remains entirely theoretical. Having them burst into song and dance to Frank Sinatra tunes may satisfy Ephron's yearning to make a '50s-style romantic comedy, but it doesn't help matters. By the tepid ending, the movie appears to have been sedated.

Still, Kidman and Ferrell are a kick to watch. Wisely, she doesn't try to ape Montgomery. Unwisely, she seems at first to be channeling Marilyn Monroe, overdoing the breathy, little-girl voice. But once Isabel gets the part, Kidman settles into a bright comic groove. Ferrell--bewitched, bothered and bewildered--loosens her up. His character, part monster and part pussycat, barely makes sense, but Ferrell's inspired clowning more than compensates. He makes Jack's out-of-control egotism seem sweetly hapless. The spell "Bewitched" casts may evaporate before it's over (witchcraft isn't what it used to be), but the laughs it does supply are nothing to sneeze at.