setting up Server 2k3 for secure internet access

I would like to setup my server 2k3 for DSL internet access for XP clients that log onto the server.

Does anyone have any tips on this as well as implementing security?

I will setup DHCP/DNS via DCPROMO on the server and disable DHCP on the router. Just wondering what securety measures I can place on the server, or at least what my options are?

Thanks