How does one set-up a LAN for gaming?

Depending on where the PCs are, you need to decide between Wireless and cabled LAN. if you are going to have all the equipement in the same room. Go with a cabled LAN, it's cheaper and a lot more stable.

(1) Get all the LAN cables and nework cards you need. Oh and a Network Switch, remember you need one port on Switch per LAN connection. So the number of ports depends on the number of PCs ou expect to connect.

(2) Connect all the PCs to the switch and assign an IP address to each network card (open Network Connections in Windows). Use the 192.168.1.X or 172.16.1.x range. Keep the subnet as 255.255.255.0

(3) Test yor connection by PINGing other PCs.

That's more or less it. I don't know if you'll have to run a server version of the game on another PC. I've played BF Vietnam without a server with 1 PC connected straight to another, just ONE lan cable connecting both (you need a switch for more than 2 PCs). Let us know how it turns out.