In other words, I want to know if it's possible with WorldForge server part to connect multiple servers, so that they work as a single logical unit ? I think its about clustering and load balancing but I'm not sure...
No, there is no current support for horizontal scalability, though great progress was made last summer towards supporting server sharding, and teleporting between servers.
I think about clustering support a lot, but the load we are currently seeing on the live servers does not justify much effort on scalability while there are so many other projects to work on. Feel free to drop into IRC during the UK working day to chat to me about this subject if you are interested.
My working day typically starts around 10am UK time, and I work until 6:30pm UK time. I don't know where you are based, but it should be fairly simple for you to work out the time offset.