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This paper discusses the important role of multicasting in designing, implementing, and managing interactive multimedia distance learning systems. This is achieved in the context of IRI, an Interactive Remote Instruction system for distance learning built at Old Dominion University. IRI is an Internet-based system which integrates continuous multimedia, shared applications and a variety of multi-user collaborative utilities. In this paper, we concentrate on the process architecture and dynamic multicast group handling as they pertain to managing multimedia resources, and show how they support robustness and short response time to user actions. IRI uses raw IP multicasting for audio and video streams and reliable multicasting for resource management and data sharing. The system is scalable (uses multicast for inter-process communication) and expandable(partitioned into a setof autonomousbutcooperating components).