At the prompt type :-
ifconfig eth0 10.0.0.1 netmask 255.255.255.0 up
Assuming you are configuring your eth0 card, replace it accordingly if there are more than one nic in the machine.
The "up" at the end of the command activates the interface. To make this permanent each time you boot up you'll have to add this command in your /etc/rc.d/rc.local file.