This is taken from a Post by Sam to the "SUITS forum". It describes how to set up a transparent proxy for when inside the university network. The attached file squid_config.tar.gz contains the referenced squid configuration details.
So, I've worked out how to set up my MacBook to automatically proxy connects to port 80, when I'm inside SIT. (yes, I know, it's only specific ports - but its a nice start). It's a giant hack, as James sitting next to me is pointing out, but I like it. This should work for Macs, and other Unix-like systems (although you'll have to change 'ipfw' to the command for your system).
You've got to install squid somehow, which will do most of the work connecting to the upstream proxy if required. I've attached my config file (The most relevant part is probably in cache_peer). This currently works for users on the postgrad network only. You could further update the cache_peer config to include your login for the general UCC network, though, and you'd also have to change the targeted IP range (which is in the config lines below).
From then, you have to both forward all outbound traffic (from a University IP range, i.e. when you're on the network there) to the transparent Squid proxy, and at the same time, allow all traffic from uid squid out (otherwise you get an infinite loop, where squid tries to proxy itself).
You then have to run these two commands to connect everything up: (note that 129.78.114.0/24 represents the range at which this forwarding takes place)
sudo ipfw add 00900 allow tcp from any to any dst-port 80 uid squid sudo ipfw add 1000 fwd 127.0.0.1,3128 tcp from 129.78.114.0/24 to any 80
And then running 'sudo ipfw list' should give you this:
Mac@MacBook ~ $ sudo ipfw list 00900 allow tcp from any to any dst-port 80 uid squid 01000 fwd 127.0.0.1,3128 tcp from 129.78.114.0/24 to any dst-port 80 65535 allow ip from any to any