Packet Sniffing problem

Hello there,
I am trying to packet do some packet sniffing on a small network as the to monitor website traffic. I am using cain and able to do this, and am having a problem with one of the computers.


I can see all the but one of the computers traffic. This particular computer is running its traffic through an external proxy server at the local university, so when I am trying to packet sniff the traffic from this computer it only shows packets coming from the single external proxy server, not the individual websites. So therefore i can't see the actual website this computer is visiting. Would anyone be able to help me on this?

The network setup has is four computers behind NAT router.

Thanks

 

Chances are if its proxying information, you shouldn't be sniffing it? Anyhow i know of no way to sniff it with out being on the other side of the proxy.