The pair, who play a criminal suburban couple, wear disguises (one was Sonny and Cher) as they rob people.
Originally, the actress says, Carrey was to play Sonny -- but she suggested they swap roles, since he's taller.
"Jim is a beautiful man, and quite sexy, but he makes the most bizarre-looking, transgenderish woman!" she says with a laugh. "I thought it was the freakiest moment when he walked in wearing that dress and wig. His hair kept catching in his lipstick."
Carrey, a master of physical comedy, was happy to have found a worthy comic partner in Leoni, who's done her share of pratfalls in films like "Flirting with Disaster."
Leoni says she loves the spills she takes in "Dick and Jane" -- especially a scene in which she falls over a table in a coffee shop they're robbing.
"I'm extremely proud of that move," says Leoni. "On the first take I put up some biscotti, and took those down. But it didn't look painful enough. And then I found some thermoses, and I set those up too. I wanted it to be perfect -- like bowling."
Her tumbling impressed Carrey, who's equally clumsy in the film.
"I love Tea, she's a total gamer. She'll do anything, go anywhere," he says. "That was the fun thing about the movie. That, and showing white-collar creeps what it's like to get reamed."
"Dick and Jane," a remake of a '70s film starring George Segal and Jane Fonda, blends slapstick with a look at how corporate greed has derailed the lives of countless Americans over the past five years.
"I think the way we handle it is funny, but the story is not. Enron was not funny," says Carrey, who also produced the film. "But hopefully this is a bit healing. They get their comeuppance."