Unless they are overplanning/controlling, Paul, using a proxy server for port 80 and blocking everything else, then I would imagine that they use NAT just like everyone else on the planet (universities, etc. excepted). Since they prolly have more outside IP's than internal users, then you just need to know how to find out your external IP. You can do this any number of ways, but I find http://whatismyip.com is very handy.