Helping people with computers... one answer at a time.
It's possible to network two computers with just a cable, but there are a few tricks involved to get things working properly.
Can I network two computers with just a cable?
BUT ... it's easy to get it wrong unless you know a couple of tricks. But once it's working, it's a very quick and handy way to transfer files and share an internet connection among just two machines.
There are two simple tricks:
First: a regular network cable will not work. You need what's called a "reversing" or "cross-over" network cable. The problem is that a regular cable will connect the transmitter of computer A to the transmitter of computer B, and the receiver to the receiver. What you want is the "reverse" - you want the transmitter of one computer connected to the receiver of another. (Hubs, routers, and the like know to listen to the transmitter, and send to the receiver - so "normal" cables work just great when you're connecting to those.)
Second: you may need to install an additional network protocol. If all you're doing is connecting two computers, you may need to install either the IPX or NetBEUI protocols. It's more complicated than is necessary to get into here, but these protocols allow computers to identify themselves, rather than relying on some other device to assign them an address. In this case things that rely on TCP/IP will not work. However, if you use Internet Connection Sharing on one of the computers to share a connection, then TCP/IP, and all the tools that rely on it, will work and no additional protocols will be required.