Hi All
Thanks you all (both on and off list) for your answers. I thought there
would be an easy answer and it looks like there is.
So instead of connecting the ADSL modem to the Airport Extreme Base
Station's Ethernet (LAN) port (which I was doing) I should connect it
via the Ethernet (WAN) port (ie the 10/100Base-T port). Then all I have
to do is buy a new Ethernet cable and connect my non-airport Power Mac
G4 via the the Ethernet (LAN) port.
Okay, so this information is in the manual, but when you are not that
savvy, it's not all that clear.
Regards Joe