TONIGHT'S MUST-SEE

Olympics, 6 p.m., NBC. This was supposed to be the big day for the host country, with Liu Xiang as the favorite in the 110-meter hurdles. He had to withdraw, however, because of a hamstring injury. Also lost to injury is U.S. hurdler Terrence Trammell. The event — now wide open — is one of many track finals. Women have the 200-meter dash; men have the 400-meter run, the triple jump and the first half of the decathlon. Other finals are in women's 10-meter platform diving and men's beach volleyball.

TONIGHT'S ODDITY

"The Principal's Office" debut, 6 and 6:30 p.m., Tru TV (Oceanic Cable Channel 19). For its first half-hour, this reality show is addictive fun. We see lots of teens in their principals' office; most are amiable chaps with lame excuses. The next episode reminds us that unquestioned power can be scary. One principal follows his rule book so rigidly that a student must stay in school after vomiting twice. If she leaves, she can't go to the prom.

OF NOTE

"Ugly Betty," 7 p.m., ABC. Wilhelmina schemes anew when Daniel dates her sister.

"Tabatha's Salon Takeover" debut, 7 p.m., Bravo. Each week, Tabatha Coffey ("Shear Genius") transforms a struggling hair salon. Her opening task is immense: An attractive married couple spent $750,000 on remodeling, with an oddly ugly result. Also, a 5-inch-thick manual robs employees of spark. Coffey arrives as the place nears financial ruin.

"Grey's Anatomy," 8 p.m., ABC. George and Lexie try to like their awful apartment.

"CSI: Crime Scene Investigation," 8 p.m., CBS. Six showgirls have been killed.

"MVP: He Shoots, She Scores" season finale, 8 p.m., Soapnet. Last week's hour was wretchedly excessive; this one hits extremes, but has good moments. The best is the sweet pairing of Gabe and Connie; the worst involves the mad Damon Trebuchet. Meanwhile, Evelyn searches for her daughter.