look for a file called ifcfg-eth0
it is in /etc/sysconfig/network-scripts/

use "locate ifcfg-eth0" to find it if nescessary.

That is the file that you will need to edit in order to set the IP manually.

it should look something like this....

DEVICE=eth0
USERCTL=no
ONBOOT=yes
BOOTPROTO=none
BROADCAST=192.168.1.255
NETWORK=192.168.1.0
NETMASK=255.255.255.0
IPADDR=192.168.1.5

You will also need to mess with

/etc/sysconfig/network

to set other needed settings... it should resemble

NETWORKING=yes
HOSTNAME=name.host.net
FORWARD_IPV4=yes
GATEWAYDEV=
GATEWAY=192.168.1.254