Chicago co-stars Catherine Zeta Jones and Queen Latifah are to perform a duet at the toned-down Oscar ceremony.
Zeta Jones is due to give birth two weeks after the Oscars
Zeta Jones will take to the stage on Sunday to sing a song from the movie despite being eight months pregnant.
Both Latifah and Zeta Jones have been nominated for an Oscar in the best supporting category, for their performances in Chicago.
The organisers of the Academy Awards have said the ceremony will be a less glitzy affair to reflect the war in Iraq.
This year stars will not pose for pictures or interviews on the red carpet and the ceremony itself will be a more sober event.
There will also be no seats for fans outside the Kodak Theatre, in Los Angeles, one of the traditional elements of the Oscars.
Hollywood's reaction to the decision was mixed.
"I really was stunned and very disappointed. We've let Saddam Hussein push us around one more time," said Johnny Grant, Hollywood's honorary mayor.
But star Arnold Schwarzenegger, known for his hardman roles, said the move made sense. "I think it's a good idea to try to eliminate the red carpet and also try to eliminate all the political speeches."
Queen Latifah plays Mama Morton in Chicago
In a further development, actor Will Smith, who was due to present an award, has said he will not be attending the event because of the outbreak of war with Iraq.
During the event Zeta Jones and Latifah will perform I Move On from Chicago, which is nominated for best original song.
Zeta Jones is due to give birth to her second child with husband Michael Douglas two weeks after the Oscars.
It is expected that an ambulance will be on standby outside the Kodak Theatre in Los Angeles in case the baby arrives early.
Singer-songwriter Paul Simon will also be performing a rendition of his Oscar-nominated song Father and Daughter from the Wild Thornberrys Movies.
Irish rock band U2 will perform their The Hands that Built America number from Gangs of New York.
The awards themselves, which seem increasingly irrelevant, are likely to be dominated by the musical Chicago - which is a firm favourite to take best picture. Britain's best hopes are Daniel Day Lewis (Gangs of New York) and Zeta Jones.
The nature of the televised show has not yet been finalised as producers discuss how best to cover the war.
The ABC network, which screens the ceremony, said it may break from the Oscars to give viewers news updates or provide up-to-date information at the bottom of the screen.
Bryce Zebel, producer of the Emmys, cancelled on the day bombing started in Afghanistan after 11 September, said: "It's going to be very difficult juxtaposing images of a nation at war with images of an awards show."
The Oscar producers have said the winners will be given 45 seconds to say anything they like - comments on the war will not be banned.
A press conference will be held on Friday to announce any changes to the schedule.