Mac address is a network address to the network card (PCs have them to).
In Tiger Apple Menu/System Preferences/Network/ select to show the network port in quesiton i,e, airport or fixed Ethernet, fifth tab to right hand side "Ethernet" and the ethernet ID is then the number you want.
But that hotel has a very odd way /labour intensive way of setting up net access for guests. Most use some proxy and a temporary ID.