This page gives details on the setup of my home network. It took a little time to get everything working nicely; perhaps this example will be of use to other people working with similar configurations. The network configuration is as illustrated below:
I get internet access via Time Warner Cable's RoadRunner service. The cable model (Toshiba PCX1100U) has both 10BaseT and USB connections; I'm just using the 10BaseT. The cable modem acts as a DHCP server for the single IP address to which I am entitled.
I have a pure-macintosh setup at home, consisting of an old Apple PowerMac 7500 (which has a 10BaseT ethernet socket), and two Apple Macintosh Powerbooks (a Pismo Powerbook G3 and a Titanium Powerbook G4), both of which have airport cards. Before I got the airport and the second Powerbook, I needed to split the internet feed, so I got a Linksys Etherfast BEFSR41 4-port bridge and Network Address Translation (NAT) box which worked very well.
When I decided to go wireless, I bought an Apple Airport Basestation. This can be connected directly to the cable modem, but there would then be no way to attach my non-wireless PowerMac 7500 to the network. So instead, I kept the LinkSys in the network, and connected the base station to that. But now we have complications: both the LinkSys and the Airport base station can provide IP address distribution (via DHCP) and IP address translation (NAT). Which should do what?
The solution I have running now, which seems to work well, is to have the LinkSys handle NAT, but all the DHCP is provided by the Airport. Since the LinkSys will translate any IP addresses in its subnet (i.e. 192.168.1.x), it doesn't matter how those addresses are distributed - I have my 7500 and one of the powerbooks configured with arbitrary static addresses (which helps for port-mapping of incoming TCP access), and the other one gets an IP address via DHCP (from the Airport).
However, it is very important that all the addresses are in the 192.168.1.x subnet. So the Airport base station has its IP address set manually to something in that range, and its DHCP range is also set to be in that subnet.
Because the Airport is not performing any address translation or packet filtering (as far as I understand), the powerbooks are able to communicate with the powermac over AppleTalk too, so I can use the powermac as a fileserver (using AppleShare) and as a printserver (using "share this printer" for my Epson Stylus Scan 2500). I don't think I can actually share the scanner, but I can also run the Virtual Network Computer (VNC) server on the powermac, and then control it via VNC clients running on the laptops. I used this to send a fax from the powerbook: transferred the file to the powermac (whose GeoPort modem is connected to the phone line), then used the apple fax software to print it to the fax line, driving the powermac via VNC on my powerbook.
It seemed like several earlier network configurations that should have worked didn't, and even when it was working, certain interactions would be incredibly slow. I'm not sure this is related, but since I upgraded the LinkSys firmware from 1.33.1 to 1.39, everything has been much better (I've stayed clear of 1.40, though, after reading comments about how it slowed everything down).
Powering up: I read on the net that an airport used with a cable modem can sometimes get into nonfunctioning states depending on the power-on sequence. The recommendation there, which has worked for me, is to power on the Airport first, then turn on the cable modem after the Airport has stabilized. I would also turn on the Linksys before the cable modem.
However, since my airport power supply capacitors died (meaning I had to implement the fix described here), I've taken to powering down my AirPort overnight, which I do by switching the powerstrip feeding all three devices (cable modem, linksys switch and airport basestation) on and off. Thus, I am regularly powering them on simultaneously, and net access is coming up absolutely reliably.
This photo shows the wires going into the three units (cable modem on the bottom, then linksys, then AirPort basestation on top). Note that the cable modem plugs into the WAN port of the LinkSys (black cable), but the AirPort just plugs into one of the four LAN ports (NOT the last `extension' port).