Can you try using the card some other way?
Xircom PCMCIA Ethernet Adapter Issues
Problem installing a Xircom CBE2-100 on an IBM Thinkpad 1400 i-sries (Khalid HASSANI)
Date: 2000, Jul 10
From: David Hinds <firstname.lastname@example.org>
I think pppoe is a difficult thing to use for diagnosis if you don't
yet know if the card is operating properly. I would try simpler
things like using the modem as a regular modem, and using the ethernet
on a regular ethernet.
to: "Can you try using the card some other way?"