ARLINGTON HEIGHTS, Ill. - What trainer Louis Roussel saw in Zarb's Magic over the winter at Fair Grounds wasn't visible to everyone. Zarb's Magic, a stakes winner who had fallen off the map, had withered down to skin and bone. A few days after Roussel bought him privately, Zarb's Magic stood listlessly in his stall, threatened people who tried to handle him and practically refused to train. The winner of the 1996 Arkansas Derby and $780,456 could not even win a $10,000 claiming race.