Two-dimensional Monte-Carlo computer simulations have been implemented to help explain some of the mechanisms responsible for structures observed during the deposition of fullerite (C-60) films on mica and glass over a temperature range from 20 to 300 degrees C. The crystal structures grown by thermal evaporation were investigated by Scanning Force Microscopy and direct comparisons were made between the experimental results and the simulations. A model is presented which is a modification of diffusion-limited aggregation but which allows for diffusion of particles within a cluster as well as cluster diffusion over the surface. The number of islands which form at different coverage, are given by the relative speed of diffusion of clusters of different sizes over the surface and the shape of the islands by the relative rate of diffusion of the molecules within a cluster. Dynamic computer visualization of the growth models assist in the understanding of the processes involved.