Don't know anything about forsight, but I can give you generic advice.
I assume that you connect either a seperate router/firewall or a cable 'modem' thru a ethernet cable and everything is normally configured thru DHCP automaticly.
So I know the generic way to get it working using command line...
1. Become root:
login as root, or
su -
or
sudo su -
2. check to see if the ethernet card is detected and activated:
ifconfig -a
or
dmesg |grep -i eth0
if you find a eth0 device then that means at least one ethernet connection is present.
3. configure the card thru DHCP detection..
dhcpcd eth0
or
dhcp-client eth0
or something along those lines.. Different distros use different dhcp clients.
or if you want to configure it manually...
Replace these ip addresses with your own:
configure nic address:
ifconfig eth0 192.168.0.11
configure default gateway:
route add default 192.168.0.254
and then make sure that you have a dns server ip address in your /etc/resolv.conf file..
make sure that it has a line similar to:
nameserver 192.168.0.254
see:
man dhcpcd
man ifconfig
man resolv.conf
man route
man whatever...
that's about it. Some cable companies require special computer id for configuring the computers thru their own dhcp servers so that could be it. I don't know. Maybe try the foresight mailing lists or whatever help they provide and ask them about it.