Use the following steps to configure ip address in Ubuntu :

Ethernet interfaces are identified by the system using the naming convention of ethX, where X represents a numeric value. The first Ethernet interface is typically identified as eth0, the second as eth1, and all others should move up in numerical order.

Step 1:
ifconfig -a | grep eth
eth0 Link encap:Ethernet HWaddr 00:15:c5:4a:16:5a

step 2 ;

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:c5:4a:16:5a", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:c5:4a:16:5b", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

Step 3 :

sudo apt-get install ethtool

ethtool is a program that displays and changes Ethernet card settings such as auto-negotiation, port speed, duplex mode, and Wake-on-LAN. It is not installed by default, but is available for installation in the repositories.

Use the following command to verify ip address configuration :

sudo ifconfig eth0 10.0.0.100 netmask 255.255.255.0

You can also verify your new ip address by using http://www.ip-details.com/