The actress got her liberal view on monogamy from her hippy parents.
She explained: "They were really liberal in the early years.
"Our house was always full of artists and musicians and I knew from the
start my parents were naughty and did things that other people's parents
didn't."
Sienna, 24 - who stars as Edie Sedgwick in new Andy Warhol movie 'The
Factory Girl' - has also spoke out about forgiving cheating Jude, 33, for
his infidelity.
Speaking at a Pepe Jeans party in London, which the couple attended together
on Wednesday night (06.10.06), she said: "The only thing I know is that Jude
is just my dear friend.
"I care about him. Our relationship has been though very difficult times and
there's something inside me I don't like about it now. There are thing that
will never be the same."

In other news, Miller, who has been in Pittsburgh shooting a film adaptation of Michael Chabon's novel The Mysteries of Pittsburgh, says she's already worried about getting older. "It's so hard for women in this business. And I want to be doing this when I'm 50."

She also says she "can't wait to have babies."

"Jude has three children," she says of Law, "and I have never tried to be their mum or anything, but I've had the benefit of living with them and loving them without being the parent. But I love the idea of being a working mum and having my kid on the set."

Miller, weighed in on the trend of thinness in Hollywood, telling PEOPLE she resisted dieting for the Edie Sedgwick role.

"The director (George Hickenlooper) wanted me to (lose weight), but I can't work that hard and not eat all the food that I normally eat – and I'm a real pig!" Miller said Wednesday at the Pepe Jeans New Ambassador launch party in London. "He would come and try to snatch bagels out of my hands and I'd snatch them back."