William Monahan won the adapted-screenplay prize for "The Departed," 's saga about rival moles who have infiltrated the police and a crime gang. The film was based on the Hong Kong thriller "Infernal Affairs."
With his debut script, Michael Arndt received the award for original screenplay for "Little Miss Sunshine," directors Jonathan Dayton and Valerie Faris' tale of a family's outrageous mishaps on the way to their little girl's beauty pageant.
Arndt and Monahan are nominated in the same categories for Feb. 25's Academy Awards. Both films also are competing for the best-picture prize.
The Writers Guild gave its award for documentary screenplay to writer-director Amy Berg for "Deliver Us From Evil," a portrait of families victimized by a Roman Catholic priest who admitted to sexually abusing at least 25 children.
"Deliver Us From Evil" is nominated for best documentary at the Oscars.
"Little Miss Sunshine" co-star Steve Carell earned two guild television honors, one for writing the "Casino Night" episode of the comedy "The Office" and a second shared with other scribes of the show for best comedy-series writing. Carell also stars on the "The Office."
The guild's other television awards included: "The Sopranos," dramatic series writing; "Ugly Betty," new series writing; Mark V. Olsen and Will Scheffer for episodic drama for the pilot of "Big Love"; Nevin Schreiner for long-form writing for the Sept. 11 drama "Flight 93"; and "Saturday Night Live," comedy-variety series writing.