OK, if you have a working wired ethernet connection to a windows laptop, you should be able to connect that way using your ubuntu pc. IF you have used the ubuntu PC to connect to BT then it looks promising too so I wonder what is wrong.
There is some software built in to the router (* see below) called DHCP. Computers that attach to the router should use the router's DHCP server to work out what settings to use. You need to check that the ubuntu machine is using DHCP. You can do this from the ubuntu System menu -> Administration -> Network Settings.
If you had to change that, turn the PC off and wait 2 minutes before turning on again.
You can see if you have a successful connection by entering 192.168.1.1/ as the address in Firefox/Safari/whatever browser you are using. This should connect to the admin. interface of the router
If you are still not working, do you know how to get a terminal window in ubuntu (sometimes called a command line)? It might be Applications menu -> Accessories -> Terminal.
Enter the following line:
sudo ifconfig -a
and post the results here. If it asks for a password, enter your ubuntu user password.
Having said all that you could try the ubuntu forums for some expert help.
Good luck again!
- I am going to call the thing you plug in to the broadband socket a router. Other people might call it a modem. I am talking about the MT882 or the echolife box - try it with both if you like.