We hope to answer most questions for everyone on how to build a gaming lan.
Whether you want to setup network gaming for local or online gaming the basics are the same. You will need either a network switch, some ethernet cables, and each computer must have a network adapter. Today in the wireless age people probably want to play lan games via wireless but due to interference from various sources wireless still is not the best bet for network performance. Network performance and the least amount of lag is more important for network gaming. There are many companies that make network cards and switches. Personally I prefer Netgear for the fact that is very easy to set up compared to many. A lot of people like Linksys but there have been confirmed security issues with them and until Cisco (who recently bought them) has been able to fix the product line, I will not recommend them.
Network switches look nearly identical to hubs, but a switch generally contains more "intelligence" (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting the data packets as they are received, determining the source and destination device of that packet, and forwarding that packet appropriately. By delivering messages only to the connected device that it was intended for, network switches conserve network bandwidth and offer generally better performance than hubs.
Once you have hooked each computer up to the switch I would make sure that DHCP is running or you give each computer a hard coded IP. A lot of games used to run on IPX but TCP/IP preforms much better as far as I am concerned.
After that it is simple. Start up the game you wish to play, set one as a server, and on the others type in the address of the server and you are on your way. If you are like my you prefer online games, so you will connect your switch to a DSL or cable line and connect to a server outside your LAN.