User's mental representations and cognitive strategies can have a profound influence on how they interact with computer interfaces (Janosky, Smith & Hildreth, 1986). However, there is very little research that elucidates such mental representations and strategies in the context of interactive hypermedia. Furthermore, interface design for hypermedia information presentation systems is rarely driven by what is known of users' mental models and strategies. This paper makes three contributions toward addressing these problems. First, it describes a novel cognitive model of comprehension of multimodal presentations for the specific application of explaining how machines work, and proposes guidelines for hypermedia design derived from this model. Since the development of this model draws heavily upon research in both cognitive science and computational modeling, a second contribution is that it contains a detailed review of literature in these fields on comprehension from static multimodal presentations. Third, it illustrates how cognitive and computational modeling are being used to inform the design of hypermedia information presentation systems about machines. This includes a framework for empirical validation of the model and evaluation of hypermedia design so that both theory and design can be refined iteratively.