The world's most popular song-swapping network, Kazaa, has thrown its weight behind a plan to start billing song swappers for their music downloads.The proposal, which could finally end the days of the free lunch for millions of music fans, has been put to big US record labels at the same time as a new legitimate version of the former file-swapping giant Napster is launched in the US. Kazaa now hopes the music industry will forget past grievances and tap into the cleaned up versions of the networks that already have millions of users, rather than build their own networks from scratch."The whole effort here is to go where the consumers are, to convert all that energy to selling licensed music," said Marty Lafferty, president of the Distributed Computing Industry Association. Nikki Hemming, the Sydney-based chief executive of Sharman Networks, which runs Kazaa, said the business model offered "great hope for the entertainment industry". Mr Lafferty predicted that within four years of the big record labels adopting the plan, online music sales would outperform traditional offline sales. By that time, he forecast, 1.8 billion licensed tracks would be downloaded a month, worth more than $1 billion a month in revenue.