I don't know if this will help but what the heck...
I had a similar problem a while back trying to do the same thing...My
situation was that the line is connected and i even get to verify with user
name and password but thenit shows some garbage and finally after a minute
or so disconnects.
I then got some advice that I could configure the ppp through the
networking button on the control panel in X. It was simple enough and when
i click on hte interface ... activate..i got the connection up.
If this is of any help to you but you still want more details i can send
you the email (advice) the person gave me. If this is of absolutely no use
...you have my permission to throw it into your rash can (since e-mail is
rather difficult to burn!)
btw there is a real cool site called Linux Support Services...which is
where i got my advice from.
http://support.marko.net