Nick Lachey will host a four-night, a capella competition, "The Sing-Off," for NBC on Dec. 15, 16, 17 and 21, the network announced yesterday.

Eight groups, none from Philadelphia, will compete for a $100,000 first prize and a recording contract.

Trading 'C' for a 'P'

CBS News correspondent Hari Sreenivasan has joined the "PBS NewsHour," the program that succeeds "The NewsHour with Jim Lehrer" beginning Dec. 7.

(Lehrer's not leaving, but he'll reportedly be sharing the show with a rotating set of anchors.)

Besides anchoring and reporting for the show's Web site, Sreenivasan will appear nightly on "NewsHour," according to PBS, "anchoring a summary of the day's headlines."

A dog for Christmas?

In tandem with next Sunday's Hallmark Hall of Fame presentation, "A Dog Named Christmas" (9 p.m., Channel 3), Petfinder.com is working with 2,000 shelters nationwide to encourage families to foster pets over the holidays, reports CBS.

Details are to be posted at Petfinder.com/fosteralonelypet.

'Robin Hood' nearly done

The third and final season of BBC America's "Robin Hood" airs Dec. 5, just weeks before the Season 3 DVD arrives in stores Jan. 12.