Real-time embedded systems must operate reliably and predictably from both a functional and dynamic point of view. To achieve these objectives we need to use an integrated approach to the design of systems. Integrated, that is, in terms of designing the hardware and software as a co-design operation. In this paper, we present a co-design tool for the evaluation and demonstration of real-time system architectures and performance trade-offs. The tool enables simulation and animation techniques to be applied in the analysis and early design stages of a project. It is specifically intended for use with multiprocessor systems to determine the optimum task allocation strategy. Allocations must consider task priority, timing characteristics and node utilization. This is achieved by the application of a stochastic global search technique based on genetic algorithm (GA) principles. Solutions produced by the genetic algorithm can be simulated and presented graphically to allow users to more easily estimate the quality of the allocation strategy.