Massively multiplayer online games (MMOGs) are becoming increasingly popular today. However, even high-budget titles like World of Warcraft that have gone through extensive beta-testing suffer from downtimes because of hard- and software problems and lags on overloaded servers. Our approach is to use structured P2P technology for the server infrastructure of massively multiplayer online games to improve reliability and scalability of these applications. Structured P2P networks are able to adapt to the current state of the game world and handle uneven distributions of the players. For load balancing, we propose algorithms based on the virtual server concept.