Just to check, when you said installed ethernet, did you plug a network cable from the modem to a network port on your computer?
Of the two options it should be the easiest as it will show up as a network connection, plus it's less annoying and resource intensive than USB ADSL modems.
First thing, make sure the network connection on your computer is set to recieve IP address by DHCP. To do this right click your network connection, pick "advanced" then highlight "TCP/IP" pick settings and check that the "assign IP by DHCP" option is ticked.
You should be able to login to the router, through your web browser and get all your setting for BT Openworld. Once done, all should be working fine.
If it isn't you could have a dud.
Try that and let me know how you get on and I'll see if I can think of any other solutions.