/etc/networking/interfaces and put the following:
# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
# The loopback interface
iface lo inet loopback
# The first network card - this entry was created during the Debian installation
# (network, broadcast and gateway are optional)
iface eth0 inet static
The last section is the most important, the top may or may not be the same so don't play with it unless you get an error. In this case the IP of the server is 192.168.1.10 so if you run it as a DNS server for example, you can set that in your router's config and not worry about it changing.
To apply this configuration type /etc/init.d/networking restart
You'll get a message that it's restarting the network interface, then you'll get booted off ssh (because the IP changed) so reconnect using the new IP and it should work.
In red hat this file is /etc/sysconfig/network-scripts/ifcfg-eth0 and you would put this in it: