I assume you have an external ADSL modem or router. You should only have two network adapters: one that plugs into the LAN and the other into the ADSL modem, the ADSL modem then connects into the phone line. What are you using the third for?
I also assume that you have a dynamically assigned IP address for the ADSL connection (ie you're on the home network and not paying for a business connection). Make sure under network properties for the ADSL adapter that you have not assigned an IP address to that adapter. If you're not using DHCP for your private network, you can still assign IP addresses to your LAN adapters, but the ADSL adapter should use DHCP (from Telstra's side).
Finally, have you removed all the modem drivers and TCP/IP settings etc?
