Filming Stephen King's The Tommyknockers in New Zealand felt like a homecoming for Marg Helgenberger. She didn't grow up there, but the remoteness reminded her of North Bend, Neb. (pop. 1,249). ''I'm not dissing my hometown, but I wasn't exposed to much,'' says Helgenberger, 34, who won a 1990 Emmy for China Beach. ''When I went to (Northwestern University), it was the first time I had ever gone to school with a black, Jewish, or gay person.''
Helgenberger's Tommyknockers character gets exposed to something even more eye-opening: A UFO turns her into a pale-as-death zombie with missing teeth and glowing green eyes. ''There was something exotic about the way I looked,'' she says. ''I didn't think I was ugly although most of the crew did.''
Helgenberger's role as Debbie Banister in CBS' true-crime drama, When Love Kills: The Seduction of John Hearn (May 18-19), required only inner ugliness. ''She was an ace liar,'' Helgenberger says of Banister, who convinced her lover to commit murder in 1985. ''It was an art form with her.''
That wasn't the only art form Banister mastered. ''She had a way with oral sex,'' Helgenberger says. And how will this be handled on CBS? ''With a lot of discretion,'' she says. ''I don't know if some of it will make it to the screen.''
Helgenberger's love scenes with Kills costar Gary Cole didn't trigger legal action from husband Alan Rosenberg, 42, whose Civil Wars' character may move to L.A. Law next season. ''Alan never came to the set for those scenes,'' she says (the couple has a son, Hugh, 2). ''But he's an actor he understands.''
Helgenberger hopes her double dose of May movie madness will elicit ''a good reaction'' from audiences. With a laugh, she adds, ''As opposed to overexposure.''