Plain simple:
Assuming all the PC's u have a NIC, buy a hub/switch with enuf ports & connect all your pc's to the hub via straight (straight crimped cables) cables.
The server must have two NIC's, one to connect to the local network & one to connect to the internet. Share the server's internet connection. It'll automatically create a DHCP sever on the server machine & it will assign IP addresses to the PC's in the network. Your network is ready..
