hello,
I made this network of 20 computers and i think im behinde a firewall cuz of my proxy server and i cant get msn voice chat work from the net work to any computers outside the network my proxy server is proxy1.emirates.net.ae so if u could help me with that i would more than happy thanx alot

I think that things such as file transfer and voice chat require at least one of the users to be able to accept incoming connections. Since your network is behind a firewall + proxy incoming connections cannot come in. I am not sure if there is a workaround other than just using an ordinary telephone.

Real-world (non-computer explanation) example: William cannot accept incoming calls on his telephone. Therefore he must call others in order to talk to them. Alfred cannot accept incoming calls either. So, Alfred & William cannot talk to each other becuase neither of their phones will ring.