Some stuff, like monitors and keyboards, can't easily be shared over a network. Things like modems, hard drive space, and printers can easily be shared among computers, saving time and money. If you're a game freak, networking your computers allows you to play games against one another a lot easier, too.
There are various aspects of networking your computers together that I will touch on here: hardware, software, and TCP/IP.
Other things to look for in network cards include: 10-Base-T and BNC connectors. The 10-Base-T connections look like a larger phone cord-type connector and a BNC connector is round and sticks out about an inch from the back of the network card. This gives you quite a bit of flexibility in terms of how you want to hook your computers together. I also like software configurable network cards -- not necessarily plug 'n play types. Software configurable cards allow you to easily reconfigure your network card without having to open up the computer.
The next choice you have to make is: what kind of cabling should you use? Though it will depend on the network cards you choose, this decision may dictate the type of cards you buy. For a small number of computers a short distance apart, BNC connectors (aka Thin Ethernet) is the way to go. With BNC cabling, all the computers are connected via a series of BNC cables and "T" connectors. The BNC cables are run between each computer on the network. The "T" connector is required to phyisically hook the compuer up to the network. At each end of the network, you need a "terminator," which is necessary for the phyiscal properties of the network cabling to function properly. To add another computer to the network, simply remove the terminator, stick another BNC cable with another "T" connector, and hook the terminator to the "T" connector you just added to the network.
Hooking up computers with 10-Base-T is slightly more expensive as you have to purchase a hub that each computer on the network must plug into. Also, since each computer must physically connect to a central location, you will need more cable than with a thin ethernet network. But a 10-base-T network is what is used in most companies and allows for greater expansion than thin ethernet networks. If you run out of ports on your 10-base-T hub, you can simply purchase another hub and daisy-chain the hubs together or purchase a larger hub.
You can also do a two-computer 10-Base-T network without a hub, however. You use what is called a "Cross-over" cable to connect the two computers together. These cables are no more expensive than regular 10-base-T cables, though they often have a different colour so that you don't confuse it with a regular 10-Base-T cable.
For the non-technies, there are companies out there that sell a "Network in a Box", which includes all the necessary equipment to network computers together complete with hardware and software. There can be some savings in purchasing one of these packages, though do the math to make sure you're not getting ripped off.
For the curious, most of my computers have Ether16 Lan Cards made by LinkSys, which I have found to be quite reliable. One thing that's cool on the LinkSys site is a series of pages on "How to Build a Network," which has some good information for beginners.
The main thing to worry about in networking computers is making sure they all talk the same network protocol. When you install a network card on Windows 95, the default protocols are NetBEUI and IPX/SPX. NetBEUI is a protocol that is only available on things running a Microsoft OS, but it nice in that it requires no setup. IPX/SPX was developed by Novell for use with their Netware product. The most cross-platform protocol to use is TCP/IP. I will discuss more about TCP/IP next week.
Once you've configured your network cards and protocols, you will need to make the desired resources on your computer shared. On both Macs and Windows systems, you will need to make sure you are set up to share files and printers. You should configure these resources with a password. Each time you need these resources from another system on your network, you will have to identify yourself with a password. Once you've done that, the resources will be available just as if you were sitting on the computer they are really attached to.
You will not be able to share resources between a PC and a Mac without additional software. While you can make the Mac and a Windows box talk the same protocols, they do not share files or resources the same way.
On a system that connects both to the Internet via a modem and a local area network (LAN for short), this machine will have two network addresses associated with it -- one for the dialup connection and one for the network card. Machines on your LAN will talk to your machine via the IP address of your network card. When you talk to the Internet, it will use the IP address of your dialup network interface.
Usually, the IP address for your dialup network interface is assigned to you by your provider, sometimes right when you dial in. Other information like subnet mask, default route, and DNS information will also be given to you by them. For your network interface connected to your LAN, you will need to assign this yourself. Unfortunately, you can't just pick anything or you will not be able to talk to both the Internet and your LAN. Fortunately, the IANA (the Internet Adressing and Naming Authority) has set aside certain IP addresses as "private" for use in situations like a home network or a large, corporate network that does not wish to talk to the Internet. Machines on the Internet will not correctly "route" or deliver packets for these "private" IP addresses. According to RFC-1918, they are: