The advantages of workstation clusters as a parallel computing platform include a superior price-performance ratio, availability, scalability, and ease of incremental growth. However, the performance of traditional LAN technologies such as Ethernet and FDDI rings are insufficient for many parallel applications. This paper describes APACHE (Automated Pvm Application CHaracterization Environment), an automated analysis system that uses an application-independent model for predicting the impact of ATM on the execution time of iterative parallel applications. APACHE has been used to predict the performance of several core applications that form the basis for many real scientific and engineering problems. We present a comparison of the performance predicted by APACHE with observed execution times to demonstrate the accuracy of our model. Finally, we present a method for a simple cost-benefit analysis that can be used to determine whether an investment in ATM equipment is justified for a particular workstation cluster environment.