Linux Thinkpad Cable Modem

Was wondering if anyone one the list uses a cable modem ?
We'll here's my problem I go thru and set up
my pcmcia ethernet card all my network setting
(dns,gateway,host,domain,whatever ) reboot
it works, sounds good. reboot again because
i just have to see what happens, Network unreachable ,
look at all my config files every things right, resave them
reboot it works boot again Network unreachable.
most of the day like this and reading the how-tos
on cable modems, pcmcia cards, ethernet cards, played
quake, now i'm going to go at it again.
Henry