Lead: 'Advocates of open source software have hailed a court ruling protecting its use even though it is given away free.' The article continues: 'The US federal appeals court move overturned a lower court decision involving free software used in model trains that a hobbyist put online. The court has now said conditions of an agreement called the Artistic Licence were enforceable under copyright law. 'For non-lawgeeks, this won't seem important but this is huge,' said Stanford Law Professor Larry Lessig.'