John Cusack and James Spader prove their mettle as actors by investing this stupefyingly naive and predictable melodrama with genuine conviction. Both play law students at the University of Virginia. The script, by the usually astute Kevin Wade (Working Girl), helps the audience tell them apart by making Spader's Tim Garrity always virtuous and Cusack's Peter Burton always awful. Garrity becomes a prosecutor; Burton, natch, enters politics. Herbert Ross (Steel Magnolias) directs this high-gloss…