Did Nike bend the rules on Olympic advertising? The ad shows people from all walks of life pursuing their ordinary sporting dreams in towns around the world that just happen to be called London. The ad has the tag line, ''Greatness is not in one special place or one special person; greatness is wherever someone is trying to find it.'' The Nike ad makes no reference to the Olympics and shows no images of Olympic events or athletes, all banned under strict new laws designed to protect official Olympic advertisers that have paid up to $100 million for the privilege. Nike's been spared, but other's haven't been so lucky.