This section describes my PC hardware, in reverse chronological order.
The network environment consists of a DSL modem connected to a wireless-G broadband router (presently a LinkSys WRT54G). The router has four ethernet connectors, and two are occupied by my Mac Pro and Linux machines. The wireless capability is nice because it supports internet in our guest room over 100 feet away, as well as incidental notebook usage around the house, and even outside.
The router provides firewall services and network address translation, etc. I turn off all outside access via the firewall so that I can be relatively lax about security on the private internal network. I might enable the ssh port for outside logins occasionally, such as when I'm traveling. Since the wireless connection bypasses the firewall, it is set to use maximum encryption.