Williams' character dies in a car crash and awakens in heaven where he begins to search for the souls of his children who died before him, and for the soul of his wife, who took her own life when she could not cope with the loss of her loved ones.

It's a dazzling special-effects extravaganza that creates awesome visions of the various levels of the afterlife.

"I believe in heaven and hell. I've had coming attractions of them in my dreams," Williams says.

"There are also places right here on Earth that, if they're not heaven, they're a pretty good start. Places like Thailand, Hawaii and Montana are gloriously beautiful"

Williams also uses Italy as an example.

"Just visit Venice with someone you love and you know what heaven must be like, but on a hot summer day when the city's septic tanks aren't working, you get a whiff of hell."

Williams feels "the world experienced hell on Earth during the fires of Kuwait and any doctor who deals with madness and psychoses will tell you they've glimpsed hell."

He maintains that "love encompasses both heaven and hell. Those people who have found their soulmates know how turbulent love can be on the way to that discovery."

This is a veiled reference to his tumultuous first marriage.

Williams met his first wife, Valerie Velardi, while he was studying drama at Juilliard in New York.

They were married for eight years and had a son, Zachary.

Their marriage was torn apart by Williams' reliance on cocaine and alcohol. Williams was with John Belushi the night the comedian overdosed in 1982.

The shock of this death and the impending arrival of his first child inspired Williams to go cold turkey, but the damage had been done.

He and Velardi never fully reconciled, and in 1984 the couple hired Marsha Garces, a young painter who'd been working as a waitress, to be Zachary's nanny.

After Williams and Velardi separated, Garces travelled with the comedian, acting as his assistant.

They married in 1989 and have two children, Zelda, 8, and Cody, 6. This is Garces' third marriage.

Williams is adamant that "Marsha did not break up my first marriage. It was broken in shambles before we fell in love and Valerie had already found someone else.

"Marsha is the one who put my life back together."

Because he has lost many friends and his father, Williams says he understands the pain that death brings to those it leaves behind.

"When you're young, death seems so outrageous, but as you get older you begin to lose people dear to you. My father-in-law is 80. There are days when he wants to go.

"I'm 47, death is becoming a more regular scenario in my life, but death is really scary for me right now because my life is so extraordinary."

Williams has his wife and family, an Oscar for Good Will Hunting and more film offers than he can handle.

He has already filmed Jacob the Liar, about the ravaging effects of the Holocaust in Poland, and Patch Adams in which he plays a doctor who uses laughter to treat terminally ill patients.

In February, he reunites with his Mrs. Doubtfire director, Chris Columbus, for the science fiction film Bicentennial Man in which he'll play a robot.

In What Dreams May Come, which opens Oct. 2, souls are offered the opportunity to return to Earth.

Williams says he believes in reincarnation

"Sometimes I feel I've been reincarnated, but I'm not like those people who claim to remember their former lives.

"I find it amazing that people were always a doctor to the Pharaoh and never the little guy who died dragging the stones to build the pyramids."

Good Will Hunting was Williams' fourth Oscar nomination. He'd got similar nods for Good Morning Vietnam, Dead Poets Society and The Fisher King.

"This year was the calmest I'd ever been at an Oscar ceremony where I'd been nominated.

"Ironically, I think that was because this was the first time I actually felt I had any chance of winning.

"In the first three instances, I was clearly the wild card, but this time I felt I had a 50/50 chance."

Williams admits his win "is a wonderful thing for my self-esteem and my career, but it is not the defining moment of my career.

"My Oscar is on Marsha's desk. She is Oscar's keeper.

"He sort of peeps out over the morning mail."

He has been approached several times to write his autobiography but he always declines.

"The truth is I don't remember enough about the '70s and early '80s.

If they'd let me start at about 1985, I might consider it."