You may need to post more information. Like is it an internal pci card or some sort of external adapter. Also what is it normally plugged into (like mine is internal pci card that then plugs to a router/modem via a 8 port hub), because if it's something like that then you would just config the eth 0 using the IP address of the router.
also, is you service provider giving you a static or dynamic IP address (static is probably easier to set up if you plug the ethernet device straight into a modem - dynamic often need's "dhcp" to work).
In fact, what type of connection/modem are you using, as there are differences between the setup that you would use for dsl and cable, or dial up?