You can try a suggestion from the HOWTO
Xircom PCMCIA Ethernet Adapter Issues
RBE-100 freezes system on startup and insertion (Julian Smith)
I'd first try a PCMCIA driver upgrade (David Hinds)
Tried that...no good... (Julian Smith)
Date: 2000, Jul 10
From: David Hinds <firstname.lastname@example.org>
The PCMCIA-HOWTO does say:
o On IBM ThinkPad 600 and 770 models with internal modems, exclude port
which is certainly worth a try.
David defeats Goliath by Julian Smith, 2000, Jul 12
to: "You can try a suggestion from the HOWTO"