Squeezing NAT Out of Panther Server
"What I wanted was very simple and very routine—so routine and simple that it's enabled with a single checkbox in Mac OS X 10.2 and 10.3. But I wasn't working with the client versions of Mac OS X. No, I was in server land. And I wanted Panther Server (Mac OS X Server 10.3) to hand out private Network Address Translation (NAT) managed addresses over DHCP (Dynamic Host Configuration Protocol)." Read the tutorial at OReillyNet.