In this paper, a simulation model for incorporation within a performance-oriented parallel software development environment is presented. This development environment is composed of a graphical design tool, a simulation facility, and a visualisation tool. Simulation allows parallel program performance to be predicted and design alternatives to be compared. The target parallel system models a virtual machine composed of a cluster of workstations interconnected by a local area network. The simulation model architecture is modular and extensible which allows re-configuration of the platform. The model description and the validation experiments which have been conducted to assess the correctness and the accuracy of the model are also presented.