There is a problem with the network manager in ubuntu 9.10, maybe a bug due to which DSL connections doesn’t work.

The solution to the problem is to use pppoeconf command rather than network manager to make a DSL connection and connect to internet.

Type in the command in the terminal make sure that your modem is powered on

sudo pppoeconf

Go through the options and keep all setings as defaut i.e go on selecting yes.
Input the username and password which was provided by your ISP (with which you login)
Your DSL connection will be setup.
To check status use the command : ifconfig ppp0

It worked for me !!