The Blood of Yingzhou District, a Chinese film about the effects of Aids, won best documentary short.
'Amazing'
Dame Helen Mirren is thought to be a strong candidate for best actress for The Queen, but she told the BBC on the red carpet that she had not been distracted by speculation over her chances.
"We know that we're not horses or greyhounds. We're not sportsmen."
"Being the front-runner or the winner honestly doesn't come into it. I haven't really been thinking about that."
She described the feeling of being nominated for an Oscar for The Queen as "amazing". "I didn't think I was that sort of actress," she added.
Martin Scorsese is tipped to take his first best director Oscar for The Departed after five previous nominations in the category.
Leonardo DiCaprio, one of the stars of that movie, arrived at the ceremony with his mother.
"She's strolling around here somewhere," he said of her. "She loves it, man. She's more excited than me."
'Excited and nervous'
US comedy star and talk show host Ellen DeGeneres is presenting the glittering ceremony at the Kodak Theatre.
She is only the second woman, after Whoopi Goldberg, to front the annual telecast single-handedly.
In the best actor category, DiCaprio faces competition from Forest Whitaker, Will Smith, Ryan Gosling, Peter O'Toole.
Penelope Cruz is up against Dame Helen, Dame Judi Dench, Meryl Streep and Kate Winslet for best actress.
Cruz - nominated for Volver - said she was "very excited and very nervous".
"I don't think I'm going to win tonight but it's just wonderful to be here."
Musical drama Dreamgirls has eight nominations in total, including three for best song, but missed out for best picture.
The films in the running for that category are The Queen, Babel, The Departed, Letters From Iwo Jima and Little Miss Sunshine.
Source : 'BBC' : http://www.bbc.co.uk/
