hello,
The client 3D rendering aspect of a MMORPG is not the biggest issue and in fact not so different than a classical 3D RPG
I think you should try to get information about network topology for such kind of applications... If you means massively multiplayer, you should be able to have more than one node/server that share a similar world , maybe look at the data grid concept (--> OGSA recommandations but it s more oriented on web services than on real time apps) or else you should have a very powerful (and probably very expensive) server....
But the first step is to be able to manage correctly your network. What do you have to send in order to ensure similar version of the world for each client??? and at the same time (synchronisation probllem)
Practically, take a closer look at the nio package in the java API. it is aimed at developing applications with high scalability... But maybe not enough to be called massive