I haven't checked how the Multiplayer will work but.. can someone explain it? I heard its alot of servers connected so one server represent 1 city in the forgotten realms.
Please explain :)

That's only one example of how it can work. ALFA will be doing that, connecting many servers to recreate the whole of Faerun.

Read the FAQ at http://www.sorcerers.net/Games/NWN/nwnfaq.htm for everything you need to know.