With the emergence of grid computing environment, performance measurement, analysis and prediction of non-dedicated distributed systems have become increasingly important. In this study, we put forward a novel performance model for non-dedicated network computing. Based on this model, a performance prediction and task scheduling system called Grid Harvest Service (GHS), has been designed and implemented. GHS consists of a performance measurement component, a prediction component and a scheduling component. Different scheduling algorithms are proposed for different situations. Experimental results show that the GHS system provides satisfactory solution for performance prediction and scheduling of large applications and that GHS has a real potential.