I use a Mac G4. I bought a DSL-300T modem which works just fine with built in ethernet and using DHCP I have also connected a DI-624 router which allows me to feed a G3 in the next room via a DWL-122 wireless adapter and an old Mac 1400 notebook using an Orinoco Gold card. Orinoco is the original producer of Apple's airport cards.
This is a very simple solution (and inexpensive as the only new unit I bought was the modem, I have 4 other modems all usb)however I did have some problems doing the configuration as the documentation which comes with each unit could be improved. The 624 can feed a number of adapters.