"Las Vegas: An Unconventional History," 9 p.m., PBS; concludes tomorrow. In the 1890s, this documentary says, Nevada was the sparsest state in the union. Its population would have fit in Boston's Fenway Park. The big change didn't come until 1931 with construction of the Hoover Dam. Workers wanted a no-rules place to spend their money. They discovered Las Vegas. The town's mission was to entertain. "It's not a deeply introspective culture," one person says in this fascinating film. There were pleasures of the flesh and the flash — some of them surprising. When aboveground nuclear testing began just 65 miles away it was treated as a tourist event. Then came the changes — the show-business acts, the Mob-owned hotels, the post-war travel boom. Tonight's hour stops at 1955, when Vegas was 50 years old. Tomorrow's film wraps up its first, flashy century. Both insert amiable portraits of modern people, from a maid to a real-estate agent.

OF NOTE

"Surface," 7 p.m., NBC. Miles' frustrated parents want to send him to a boot camp or an aquarium. Meanwhile, Laura rushes the construction of her mini-sub, so she can head to the spawning site.

"Prison Break," 7 and 8 p.m., Fox. In a late change, Fox has postponed new episodes of "Arrested Development" (with Charlize Theron as guest star) and "Kitchen Confidential" (with Michael Vartan as guest). Instead, it offers a "Prison Break" rerun at 7 p.m. with Michael making a decision that costs someone's life and a new episode at 8. The prisoners continue their plot, leading to a key cliffhanger episode on Nov. 28.

"How I Met Your Mother," 7:30 p.m., CBS. Lily (the delightful Alyson Hannigan) moves into the apartment with her fiance, Marshall. This makes Marshall's roommate, Ted, feel superfluous.

"Two and a Half Men," 8 p.m., CBS. Charlie lusts for a dance teacher and tricks Jake into taking ballet class.

"Related," 8 p.m., WB. This excellent series is at its best when it throws the four sisters together. Tonight, they scramble to keep their dad's fiancee from changing the family's Thanksgiving traditions.

"Las Vegas," 8 p.m., NBC. While a nonfiction Vegas is on PBS, NBC has this fictional version. Tonight, a priceless gem is at the casino; also, Robert Goulet sings and Criss Angel does magic.