I have a very simple solution for Ubuntu 9.10's DSL problem. In many forums you are told to change the "pppoeconf" settings. That is one part of the solution. I had the problem, that I installed Ubuntu 9.10 via Wubi and in this case the pppoeconf settings won't work.
You have to install Ubuntu 9.10 in the good old way on a separate partition.
Change the pppoeconf settings:
1) Change to root user
2) change pppoeconf settings:
3) Answer every question with "yes"
For my it is the best solution for people who have not a router.