There are quite a few mmorpg projects currently. I don't think any wide scale tests have been done yet though. I know a while ago CattleRustler, Mnemonix, and myself were involved in a project where we got 5 or 6 users in an environment. It's certainly possible to build the functionality. 1000s of users is going to take some clever coding, but 30 or 40 is definitly resonable. Check out the multisync(might be called or was called tempest.) in the program annoucements.
There's also the multiplayer plus commands that were released with the FPSC source(See the extras in the latest DBP patch 6.2b).
Java is definitly geared towards programming programs that talk to each other(multiplayer), for that's what our above project used.
Whatever tools you choose, you'll just have to learn it the best you can. For multiplayer, there is no easy or quick way to get a mmorpg done.
Hope that kind of helps.
A book? I hate book. Book is stupid.
(Formerly Yellow)