It's likely that most of you guys wanting to write this game know java. Believe it or not, Java is pretty damned powerful, and easily powerful enough to write an online game. I don't know about massively multiplayer: that requires giant servers costing thousands upon thousands of dollars.
But if you are interested in using java, you can either use the Graphics2D library or Java3D:
http://java.sun.com/developer/earlyA...d-install.html
I'm actually writing an online tank-battle game that ties into my website. It's been a rough road so far but I'm to the point where a handful of players can connect and blow each other up. I'm not sure how long I'll keep focused on this before I'm on to something else, however.