Have a look here. This should help you get started in the right direction.
You did not state what your network hardware is. I have been using adsl for over two years. PPPoE is bulit into my router. All I had to do was set up my user ID and password stuff in there.
How ever, my ISP does supply informatiopn on how to set up linux boxes; where the ethernet card in the system is connected to the ADSL modem with ethernet. So, if the above link doesn't help much, check out your ISP. If they are of no help, ( like most for linux ) post back who it is, and someone here may have information to help.