You will need to edit that file and change the configuration for eth0 to something like this :
Code:
auto eth0 iface eth0 inet static address {IP-ADDRESS} network {NETWORK-ADDRESS} netmask {NETMASK} broadcast {BROADCAST-ADDRESS} gateway {IP-ADDRESS-GATEWAY} dns-nameservers {IP-ADDRESS-DNS}
Code:
auto eth0 iface eth0 inet static address 192.168.1.30 network 192.168.1.0 netmask 255.255.255.0 broadcast 192.168.1.255 gateway 192.168.1.1 dns-nameservers 192.168.1.1 (google dns also works)
source: http://www.linuxquestions.org/questions/linux-networking-3/static-ip-%3D-no-internet-888974/