Diseases such as HIV which spread through direct physical contact --- either sexual interaction or the sharing of needles by injection drug users --- may be modelled by treating transmission as a stochastic contact process on the edges of a complex network. In addition, risk behaviour which contributes to the spread of HIV may also spread through social influence on this network. The example of the SIR model on a network will be used to introduce some of the basic concepts of disease dynamics on networks. Simulation studies are typically required to understand the dynamics of more complicated disease models. For this reason, our group has developed the software package NepidemiX to simulate disease models on networks. A NepidemiX simulation of a simplified model involving both risk behaviour and disease transmission will be shown. We have developed a detailed model of the HIV epidemic in Vancouver's Downtown Eastside to evaluate the potential effectiveness of treatment and prevention strategies. This model is being simulated using NepidemiX. Data to calibrate and validate the model was supplied by the BC Centre for Excellence in HIV/AIDS. Some preliminary results from this modelling study will be presented.