Ubuntu/CentOS use static IP instead of obtain from dhcp

Ubuntu:edit /etc/network/interfaces

# The loopback interface
auto lo
iface lo inet loopback

# Configuration for eth0 and aliases

# This line ensures that the interface will be brought up during boot.
auto eth0 eth0:0 eth0:1

# eth0 - This is the main IP address that will be used for most outbound connections.
# The address, netmask and gateway are all necessary.
iface eth0 inet static
address 66.246.75.77
netmask 255.255.255.0
gateway 66.246.75.1

# eth0:0
iface eth0:0 inet static
address 97.107.130.169
netmask 255.255.255.0

# eth0:1 - Private IPs have no gateway (they are not publicly routable) so all you need to
# specify is the address and netmask.
iface eth0:1 inet static
address 192.168.133.234
netmask 255.255.128.0

CentOS:
edit /etc/sysconfig/network-scripts/ifcfg-eth0

# Configuration for eth0
DEVICE=eth0
BOOTPROTO=none

# This line ensures that the interface will be brought up during boot.
ONBOOT=yes

# eth0 - This is the main IP address that will be used for most outbound connections.
# The address, netmask and gateway are all necessary.
IPADDR=66.246.75.77
NETMASK=255.255.255.0
BROADCAST=66.246.75.255
GATEWAY=66.246.75.1

edit /etc/sysconfig/network-scripts/ifcfg-eth0:0

# Configuration for eth0:0
DEVICE=eth0:0
BOOTPROTO=none

# This line ensures that the alias will be brought up when the interface is.
ONPARENT=yes

# eth0:0
IPADDR=97.107.130.169
NETMASK=255.255.255.0
BROADCAST=97.107.130.255
GATEWAY=97.107.130.1

ref: http://www.linode.com/wiki/index.php/Configure_Static_IPs