From the Olympic Games' official website

The Organising Committee for the Games of the XXIX Olympiad – Beijing 2008 (BOCOG) has started the second phase of its sponsorship programme for the summer Olympic Games, which will take place in Beijing in August 2008. The programme consists of three different levels of sponsorship, namely Beijing 2008 Partners, Beijing 2008 Sponsors and Beijing 2008 Suppliers...

...The Games organisers have put together a rights and benefits package that includes many possibilities for the sponsors to associate themselves not only with the Games, but also with the Chinese Olympic team. A sponsor recognition programme and an anti-ambush marketing programme will also help the sponsors to get the most from their partnership with the Beijing Games. BOCOG currently has seven companies that have joined up as Beijing 2008 Partners.

LINK:
International Olympic website: here
Chinese Olympic Committe website:Beijing 2008 Olympic Games Sponsorship Programme

What is 'ambush marketing'? Below is an explanation, from the website of Australian law firm Freehills:

Ambush marketing can take many forms, ranging from the conspicuous (a non-sponsor advertising a product on a building adjacent to an event venue, perhaps involving some loose reference to the event or the sport generally) to the more subtle (a non-sponsor giving away event tickets as prizes in a radio or press competition).

Ambush marketing divides opinions. Certainly, event organisers don't like it because it threatens the exclusivity of rights granted to official sponsors and risks driving the value of those rights down. Nick Bitel, CEO of the London Marathon, describes it not simply as 'parasitic marketing' but as 'marketing by parasites', and likens it to theft.

Official event sponsors don't like it much either, as it undermines the investment they have made in acquiring exclusive rights, and dilutes the effectiveness of their message in the marketplace. But even as its real victims, many event sponsors experience mixed feelings about the morality of the practice, since it is not usually too long before the next event comes round and they themselves are considering how to ambush their competitors' official sponsorships.

There are also plenty of people who admire ambush marketing, taking the view that if it is not illegal, then it is no more than the free market at work. Putting morality to one side, it is tempting to recognise it as (on occasion) ingenious and entrepreneurial, perhaps even an art form.