I've bought nwn last month and it runs fine on my computer for single player. But when i logged on to multiplayer, it won't let me join any games!!!I can see all different types of servers hosting games and the chat menu, but when i joined a game and created my own character, the computer screen just froze and it's all black, i've tried several times and still has the same problem. I have the latest patch installed and i have a P4 machine but a 56K modem.

Happenend the same for me, you've possibly got a firewall somewhere.
I dont exactly know how the firewall ports work but usually you gotta add a port at the end of the server's IP-number like 432.545.645.42:5121 <-- its the :5121 thats the port.
There are several ports to choose, check the readme manual for which ones you could possibly use.

Good luck.