using VPN and webcam settings still say I am behind a router or firewall???

I really would like to try the webcam feature with aMSN, but to date I have not been able to do this. At first I thought it was because I am behind a firewall or router -this is still most likely the reason as I'm trying to use the service from the school where I am working overseas. I figured if I pay for a VPN service that I might be able to get around this issue, but at the moment that seems unlikely also. I am still extremely confused over the fact that if I am running the windows version of MSN, using bootcamp on my macbook - I have no problems using the webcam service. What then is the problem with using the webcam in aMSN on my mac? I would prefer to use aMSN running my Mac OS instead of the windows alternative. Can anybody help me?

Cheers