Today's tween girls want to be princesses without being snobs about it. That makes Amanda Bynes the perfect star for a princess fantasy about a bubble-icious American girl who gets to wear her tiara and cast it off, too. In What a Girl Wants, Bynes hops over to England to reunite with her long-lost dashing aristocrat father (Colin Firth), who let go of her mother (Kelly Preston) shortly after marrying her in Morocco. Bynes, who worked her way up the Nickelodeon kiddie ladder before costarring with Frankie Muniz in ''Big Fat Liar,'' has chipmunk cheeks, eyes as clear as a Kansas sky, and the ability to rock out in the punkette-gymnast manner of Avril Lavigne without in any way suggesting that her knowing hip swivels are driven by salacious thoughts.
Ensconced in Daddy's mansion, Bynes shocks the stuffing out of all those fuddy-duddy English people, even as she gets the privilege of absorbing their classy airs. In her sassy but scrubbed way, Bynes is a real charmer, and ''What a Girl Wants'' is a likable throwaway. You do wish, however, that it didn't leave you with the unfortunate sight of Colin Firth, who comes off like Hugh Grant with mild indigestion, attempting to put aside his crusty ways by donning leather pants to play air guitar to ''Rock and Roll, Hoochie Koo.''