More details would be helpful, like what device is on the other end of the said network cable.
I assume for the reminder of the post that whatever that device is it has DHCP server (don't worry if you don't know what that is).
The simplest and cheapes way is to get a network switch something like this
Newegg.com - NETGEAR FS105 10/100Mbps Desktop Switch 5 x RJ45 1,000 MAC Address Table 64KB Buffer Memory - Switches or if you want wireless then something like this should do
Newegg.com - LINKSYS WAP54G Wireless-G 54Mbps Access Point - Wireless AP / Bridges. A wireless setup is slightly more hazzle than wired but nothing to worry about.
Hope this is of some help.
Zweiblumen