awww but guns would be sooo coool!
Plus a virtual world where you can kill your enemys would prevent real death in the real world =3 it can all be left in the game!
Baddie: Im gonna shoot you,,,,, as soon as i log in!
You : D:
Baddie: >

*shoots and misses*
You : >

*shoots and kills *
Baddie: (has to restart character) xD
I would play that for sure. I mean, you could gather all your friends to fight the other cliks in school! Goths vs. Preps, Jocks vs. Geeks, Heads vs. Marry Poppins Children (c'mon we all have like 5-10 in our school)
Joking aside, for a world like that, i think browser based would be your best bet.
Try unity3D or learn java from scratch.
If you want an extensive 3d application, then a regular app would be your route. Any programming language you feel comfortable in will do the job. Dark Basic Pro would be a good engine to prototype your game in, small scale testing and such. I personally wouldnt use dark basic for an mmo though. Maybe a small multiplayer fps could run on dark basic, but i havent seen alot of dark basics mmo or fps projects really come to life in the market. (and the market is what counts, it doesnt matter if you make the perfect game ever, if no one has it or wants it, its useless)