Vehicle operation simulations have a range of potential applications in research, development, training and certification/licensing. The extent of the applications will depend on the realism, validity and cost of the simulations. Advancements in PC (personal computer) and associated technologies are dramatically reducing cost of creating realistic virtual environments. Increased understanding of the computational requirements in simulating the vehicle operator's in simulating the vehicle operator's tasks allows enhancing the realism and validity of the sensor environment provided to the human operator. This paper discusses the general components and requirements for vehicle operation simulations, and the issues that influence the realism and validity of the sensory environment. two examples are described of low cost PC based simulations. The first example is driving simulator that has been used in a range of research, development and driver evaluation applications. The second example is a flight simulator for training parachute jumpers that includes realistic manoeuvring characteristics and also can represent deployment malfunctions.