At home I can connect to the internet perfectly fine with either airport, or by plugging my modem into my macbook via the ethernet cable. However at Uni we dont have wireless, so I have to connect through their internet via an ethernet cable but i cannot make it work. When I plug it in I am definitely connected to the internet, because on iTunes I am showing up with other peoples playlists who are also on the network. Network Diagnostics shows the first three nodes lit up green, however the other two are in red. I have an IP address and everything. All my friends who are connecting via the same method have everything working fine, however they're using Windows.

Any idea's whats wrong, and how I can fix it? I appologise in advance because I dont have a great deal of network experience.