Even Gellar's biggest fans should be sorry to see her in this bad career move, as a so-so chef who suddenly starts cooking enchanting meals, thanks to a magical crab heaven-sent by her dead mother. Among the bewitched is a handsome young executive (Flanery) who literally gets swept off his feet when a kiss sends him floating toward the ceiling. Theoretically Simply Irresistible is romantic; on screen the whimsy curdles like day-old crème brûlée. Re-rent ''Cruel Intentions'' instead. Better yet, save your money and catch this week's ''Buffy the Vampire Slayer.''