Tomorrow's multimedia applications will stress all parts of a computer system. To determine the computer resources needed to meet application demands we have developed a new capacity planning model that is based on application quality as perceived by the user. We have applied our model to a Distributed Interactive Simulation flight simulator called the Virtual Cockpit. We investigate the quality of the Virtual Cockpit on existing networks and processors and predict the effects of high-speed networks and high-performance processors on Virtual Cockpit quality. We find processor performance is the current bottleneck in application quality for the Virtual Cockpit, but that higher-speed networks, such as ATM, will be needed to meet network requirements after two to three generations of processor improvement.