Amber Frey (search) — whose tell-all book about her affair with killer Scott Peterson is still on the best-seller list — will be played in a TV movie by Janel Moloney (search) from "The West Wing."

CBS is moving fast to get the Frey movie done. It is reportedly aiming to finish in time to air the movie in May — during the crucial rating-sweeps period.

Filming is said to be ready to begin early next month in Vancouver.

The film, called "Witness: The Amber Frey Story," (search) is based on her book about her affair with Peterson — who told her that he was single — in the months before his pregnant wife, Laci's disappearance, then becoming the chief prosecution witness at his trial.

Moloney, who plays fast-talking White House assistant Donna Moss on the NBC series, snagged the lead role, at least in part, because she is practically a dead ringer for Frey.

Moloney, the niece of "Saturday Night Live" alum Christine Ebersole, has begun to appear in some TV movies as her role on "The West Wing" winds down.

Two years ago she co-starred in a Showtime movie called "Bang! Bang You're Dead."

The Amber Frey movie is being produced by the same people who did the TV movie about the Menendez brothers murders, "Menendez: A Killing in Beverly Hills."