So you would like to connect PCs together via a local area network (LAN) so that you can play networked games or work or whatever. With the current cost of equipment, such a network is easy and inexpensive to create. It can even be set up and torn down in a single night, so you and your friends can take turns hosting the carnage.
The first requirement for a LAN, of course, is at least two computers. The most popular way of meeting this requirement is to have somebody else lug a computer over to your house. With today's prices, however, it is increasingly possible to own two (or more) computers. For the rest of this article, I will assume you have two PCs available.
The second part of making a LAN is to have some method of hooking the computers together. The simplest way to do this is to connect a null-modem cable between the serial ports of the two computers. This costs under $10 but requires a fairly complex setup: a free serial port on both computers and software which supports this type of connection. Also, a null-modem cable limits your "network" to two computers. Odds are, you would get more mileage out of connecting your PCs via a true local area network.
A LAN-connected PC requires, at the very least, a network interface card (NIC). NICs, which cost anywhere from $10 to $85 or so, are expansion cards that look sort of like a modem or video card; they plug into your motherboard and provide a socket suitable for network cabling. NICs are distinguished from each other by their support for differing network protocols, bandwidth, and cabling.
For this article, I am going to assume that you want a card which supports the Ethernet protocol. While there are competing network protocols (I will list a couple below), Ethernet is the generally the best type of network for small, inexpensive LANs.
A NIC's bandwidth determines how quickly it can send and receive data across the network. You can choose Ethernet cards rated at either 10 megabits-per-second (Mbps) or 100 Mbps. Either one will work; 10Mbps cards are cheaper (and possibly available used), while 100Mbps cards cost more but can carry more information.
The NICs on the market today typically support one or both of two types of cabling: unshielded twisted-pair and coax. Some cards accept only twisted-pair cable, which has a connector that looks sort of like the one that connects your phone to the wall. Others accept only coax and its cable-TV-like connector. Some cards accept both types. Coax cabling will limit your network to speeds of 10Mbps.
You do not need to use identical network cards in each machine. You have to be able to use the same cable type for all of them, of course, and you will want to have the driver disk(s) for each type you use. Still, if you have a brand X card in one machine, and a brand Y card in the other, they should still be able to communicate. In fact, most 100Mbps cards will automatically drop back down to 10 Mbps when necessary -- so if you have one of each, they will still be able to communicate at 10 Mbps.
Once you have settled on building an Ethernet LAN, you essentially have some options:
Most of the $75 - $85 networking "kits" you see in advertisements or on retail shelves consist of a hub, two network cards, and two cables. If you are starting with nothing, one of these kits may contain all you need to get the first two stations networked. On the other hand, if you have already got part of what you need, you can get the individual parts quite easily.
Most of the world's office LANs use hubbed networks like these. Depending on the type of hub you get, you may be able to go as much as 100 meters from the hub on each "leg" of cable, or you may be limited to having the two longest legs measure less than 100 meters. If all your computers are in the same room, this should not matter. If you have to wire from room to room, measure carefully -- and make sure you get an "active hub" if you need to go 100 meters on each length.
Unshielded twisted-pair cable comes in different categories. Networks running at 100Mbps need a beefier category of cabling than those running at 10Mbps, so make sure your NICs, cabling, and hub are all rated to handle your network's bandwidth.
I do not recommend using a network protocol other than Ethernet unless you have the equipment on hand already. If you do, you probably already know how to set it up and can jump down to the next section. ARCnet parts are generally not sold anymore (and definitely not in retail outlets) and Token-Ring generally costs more than Ethernet.