Ubuntu Wiki

For bringing up eth0:

sudo dhclient -r eth1
sleep 1
sudo ifconfig eth1 down
sleep 1
sudo ifconfig eth0 up
sleep 1
sudo dhclient eth0
sleep 2
sudo /etc/firestarter/firestarter.sh stop
sudo /etc/firestarter/firestarter.sh start

For eth1:

sudo dhclient -r eth0 && sudo ifconfig eth0 down
sudo ifconfig eth1 up
sleep 1
sudo iwlist eth1 scan
sleep 1
sudo iwconfig eth1 essid <essid here>
sleep 1
sudo iwconfig eth1 ap <mac address of ap here>
sleep 2
sudo iwconfig eth1 key <key here>
sleep 2
sudo dhclient eth1
sleep 2
sudo /etc/firestarter/firestarter.sh stop
sleep 1
sudo /etc/firestarter/firestarter.sh start