MSN MEssanger

I want use MSN messanger for Voice & Video chatiing in my network.
I am facing 2 problems.
1)I used ICS for inetrnet sharing.i can able to speak with other computer that outside the network from the computer that connected the modem.But i cannot use voice chatting or netmeeting from any of the other client computer.

2) When i am using the network ADSL modem also i cannot able to use the Voice or Net meeting.