TONIGHT'S MUST-SEE

"American Idol," 7 p.m., Fox. On one of the few nights without Olympic figure skating, other shows can grab an audience. That's especially true of "Lost" (mentioned below) and "American Idol." This is a fairly big "Idol" night, anyway. We learn who will be the 24 semifinalists.

OF NOTE

"Veronica Mars," 4 p.m., UPN (KIKU). Someone is blackmailing the gay kids at the school.

"The George Lopez Show," 7 p.m., ABC. Veronica (Aimee Garcia) inherits lots of money, with a catch: George is in charge and doesn't have to give it to her until he decides she's mature enough.

"Freddie," 7:30, ABC. Freddie regrets losing Denise and is going after her.

"Windsor Castle: A Royal Year" debut, 8 p.m., PBS. So you thought party planning was difficult? Before Queen Elizabeth hosted French President Jacques Chirac, her staff prepared for six months. The Waterloo Room was temporarily renamed; offending paintings were removed. The "Les Miserables" cast gave a special performance. (People barely seemed to notice that a royal fortune was being spent on a musical that involved the excesses of the rich and the hardships of the poor.) This film offers a fascinating view.

"Lost," 8 p.m., ABC. Rousseau leads Sayid to a captive who may be one of the Others. Meanwhile, Sawyer blackmails Hurley into joining a mission.

"Invasion," 9 p.m., ABC. The sheriff's teen daughter — trying to figure out what transformed the grown-ups — may go into the swamp herself. Meanwhile, her stepmom resists being a hybrid. Tonight, she performs tests with surprising results.