When the Games of the 27th Olympiad open in Sydney this morning, don't expect a Nike advertising campaign about the worthless value of a silver medal.

At the Atlanta summer games four years ago, the US sportswear giant ran a controversial campaign with the slogan: "You don't win silver. You lose gold."

This unsportsmanlike message drew a sharp rebuke from the International Olympic Committee, which was upset to see one of its central tenets - that it is the taking part, not the winning, that counts most - so publicly rubbished. Nike has since become an official sponsor of the Sydney Games. But the committee is hoping for far wider changes in the commercialism surrounding the Olympics. Atlanta was something of a disaster for the Olympic movement's image. Stall-holders attempting to cash in on the games made the city seem more like a giant fleamarket than host to the world's premier sporting event.

"Atlanta is actually a great city," says Mr Michael Payne, the International Olympic Committee's marketing director.

"But what the world saw during the games was not reflective of a great city, or of the Olympic movement."

Sydney's organisers have plans covering everything from revised agreements with sporting goods companies, such as Adidas and Nike, to introducing new permits for buskers. Laws have been introduced limiting authorised food and merchandise vendors to six designated areas in the city. At the committee's insistence, the Australian government has introduced stringent restrictions on billboards around Olympic venues. All adverts bigger than five square metres must be approved by the government.

"That means we're not going to see any giant Reebok or Pepsi signs," says the Sydney organising committee. Neither Reebok nor Pepsi are official sponsors.

The International Olympic Committee has also taken initiatives of its own. A code of conduct requires sporting goods companies to consult it about their marketing campaigns. In return, the companies can make use of individual athletes' images and endorsements during the Games - something they were previously denied because of IOC-approved contracts signed between athletes and their national teams.

The result is a peculiar one. Advertising campaigns that might previously have been condemned as an unofficial "ambush" now have committee approval. For example, Adidas has launched a worldwide television campaign that boasts that Adidas-sponsored athletes will take part in 26 of the 28 sports in Sydney. Yet Adidas is not an International Olympic Committee sponsor. "We're just doing effective marketing," says Mr Rob Mills, the company's marketing director in Australia. "Our objective is not to be seen as an Olympic sponsor. Our objective is to make our brand stronger." Sydney's preparations have benefited from the fact that city, state and Games organisers are working under the guidance of a single committee. In Atlanta a quasi-corporate committee took charge of the Games but left preparations such as permits for street vendors to city officials.

Mr Payne believes Sydney will serve as a model for other Olympic host cities. For the Olympic movement and its corporate sponsors, that may be so: but the impact on the host cities may prove a mixed blessing. Leaving aside the boost to tourism and other benefits, Sydney's Games will cost New South Wales taxpayers 140 million Australian dollars (€90 million). Atlanta, for all its tacky commercialism, made a modest profit for the city. Moreover, doubts remain as to whether the clean- up will succeed. Even with the restrictions put in place, there are many signs that other advertisers plan to gatecrash the party.

Australian airlines Qantas - which is not a sponsor - and Ansett - the "official airline" of the Sydney Games - this month tussled in court over Qantas advertising with an Olympic theme.

Once the television cameras start rolling, unauthorised laser light shows and aircrafts etching logos in the skies over Bondi Beach are widely expected.

"I know there have been many non-sponsors in Sydney in the past two weeks organising what they're going to do," says Mr Martin Hirons, director at marketing research company Sweeney Research in Melbourne.

The sheer pulling power of the Olympics means controlling advertising is one game the organisers can never win.