``The Parent Trap'' is based on story elements so ancient and foolproof, they must have their roots in Shakespeare's day: the twins changing places, their divorced parents falling in love again, and, for low comedy, their servants falling in love, too. And of course there's a wicked would-be stepmother lurking about. It's the stuff of Elizabethan comedy, resurrected in modern times as the British film ``Twice Upon a Time'' in 1953, and in the classic 1961 film ``The Parent Trap.'' The story is ageless and so is the gimmick: The twins are played by the same actress, using trick photography. Hayley Mills did it in 1961, and Lindsay Lohan does it this time, seamlessly. Although I was aware that special effects and over-the-shoulder doubles were being used, I simply stopped thinking about it, because the illusion was so convincing. One twin is American, one is British, but even their accents don't help us tell them apart, since half of the time they're pretending to be each other.