By Sportswriters Gao Peng and Meng Na

    BEIJING, Aug. 6 (Xinhua) -- With two days to go before the start of the Beijing Olympics, the organizers remain tightlipped about the details of the lighting of the cauldron at the opening ceremony and the identity of the last torch bearer.

    "They are always the core secrets," Zhang Heping, director of the opening and closing ceremonies department of the Beijing Olympics Organizing Committee (BOCOG), told a press conference Wednesday.

    "Let's keep them under wraps until the last moment."

    Three dress rehearsals of the opening ceremony have been held under tight security while much of the format and props that will be used for the ceremony have been kept in secrecy.

    But the organizers did offer some information about what are in stock for Friday's opening ceremony at the National Stadium, which is better known as the "Bird's Nest" for its giant latticework structure of metal girders.

    "Chinese singer Liu Huan and British singer Sarah Brightman will jointly perform the theme song of the Beijing Games at the opening ceremony," said Zhang.

    "It will be the first time that the theme song is presented to the public."

    Liu Huan is one of the most renowned male pop singer in China, and Sarah Brightman is a classical soprano, actress, songwriter and dancer.

    Zhang also denied speculations that a segment of the three-and-a- half-hour show would be dedicated to the victims of the May 12 earthquake that hit south China's Sichuan Province.

    "The earthquake is a catastrophe for the whole Chinese nation, but we believe the Olympic Games is a grand celebration of human beings and it should not involve too many elements of sadness," he said.

    All 205 National Olympic Committees affiliated to the International Olympic Games will take part in the Beijing Games, marking a union of the Olympic family.

    Zhua confirmed that the marching order of the 205 National Olympic Committees at the opening ceremony is being dictated by the number of Chinese strokes in the first syllable of each NOC in Mandarin, a shift from the traditional system of using the first letter of each NOC.

    The opening ceremony is being supervised by Chinese film director Zhang Yimou and an international team of event planners and advisors.

    Zhang Yimou said months ago that his biggest fear was wet weather on Aug. 8, which would force him to cancel some performances in the air or some high-tech and mechanical arrangements due to safety reasons.

    "Though contingency plans for bad weather have been prepared, to our delight, latest weather forecasts predict no heavy rains on Friday," said Zhang Heping. "Thank God bless us."

    To ensure details of the event remain a surprise until the last minute on Aug. 8, design and production teams as well as the cast had to sign a confidentiality agreement before they were allowed to work on the program.

    The opening ceremony is due to run from 8 p.m. to 11:30 p.m. local time.