New York--A report issued this week by Jupiter Media Metrix Inc. says b-to-b online ad spending will decrease 10.2% this year to roughly $500 million but will rebound over the next five years. By 2006, total b-to-b online ad spending will reach $2.4 billion as more companies adopt Internet marketing, Jupiter predicts. The ad decline is a result of the softening economy, affecting both online and offline b-to-b spending. Offline b-to-b spending will total $23.4 billion this year, a 9% decline from $25.9 billion last year. By 2006, offline b-to-b spending will reach $30.5 billion, Jupiter projects.