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