Massively Multiplayer Online Games (MMOG), now supporting millions of simultaneous participants on a regular basis, have become a significant contributor in human-to-human communications. While originally designed for games, they have now moved into serious realms of socialization, business, commerce, scientific experimentation, and others. As more and more people participate in these massive environments, the underlying infrastructure is starting to exhibit shortcomings that limit the progress, practicality, and applicability of MMOGs. This thesis explores various architectural challenges inherent in MMOGs and offers effective solutions in the context of a hybrid model. The key objective of this hybrid model, realized in a Massively Multiuser VIrtual Simulation Architecture (MM-VISA), is to form a stable and scalable collaboration platform that economically combines the resources of both servers and player peers, incorporating the advantages of a centralized architecture and a scalable Peer-to-Peer distributed system, which in turn leads to improved support for the participating masses.