Several networking-related control panels from Mac OS 9 have been consolidated into Network Preferences, located in the AppleMenu --> SystemPreferences --> Network pane. Things you used to do in TCPIPControlPanel and ModemControlPanel are now done in NetworkPreferences. RemoteAccessControlPanel (or PPPControlPanel) is replaced by the InternetConnect program. Handier than the InternetConnect program is the Connection MenuExtra --just enable the checkbox labeled "Show modem status in menu bar" in the Modem tab of NetworkPreferences.
Q. Mac OS X tries to dial my modem on boot.
A. Go to NetworkPreferences, Internal Modem (from dropdown menu), PPP tab, PPPOptions button, unselect "Automatically connect when TCP/IP applications need it".
Q. Mac OS X asks me if I really want to stay connected to the Internet every 15 minutes, even though I'm actively doing stuff.
A. Go to NetworkPreferences, Internal Modem (from dropdown menu), PPP tab, PPP Options button, unselect "Ask to maintain connection".
Q. How can I change locations without going into NetworkPreferences?
A. There's a LocationMenu in the AppleMenu that lists all your locations and allows you to switch. It's not as good as the old LocationManager in Mac OS 9, but it at least switches your NetworkPreferences.
Q. When using PPP or PPPoE, the icons in the menubar will occasionally disappear, and I will be unable to restore them or access my PPP settings until I reboot. How do I stop this?
A. This problem seems to have gone away with OS X 10.1.4.
Q. Is there a way of connecting to http://localhost/ without dialing my modem?
A. Yes. Turn Web Sharing on in the SharingPreferences panel and then use that address in a web browser. Or use the equivilent IP address: http://127.0.0.1/ (this seems to avoid the DNS). Either way Web Sharing must be switched on, or some other application with a local webserver, such as Radio User Land, must be running.
Q. Can I use the built-in firewall to forbid access from the internet to the built-in web server, and still access the web server using http://127.0.0.1/ or the internal AirPort network?
A. This will require some network design. The firewall rules will need to be done on the command line, not in the GUI. Firstly restrict the IP addresses of the Airport network to something known, say 192.168.10.xxx. Now we set two rules that allow traffic from either of your networks. Then you need to setup a rule in your firewall that drops incoming packets to port 80 (or whatever the website is using). Thus only local traffic gets in, and all traffic not previously matched doesn't get to your webserver.