Firstly you need a network crossover cable. Available from most computer stores. This is a special type of cable (not a standard LAN cable)
Secondly Make sure both computers are on the same workgroup. TO do this Right click on My computer, Properties, go to the Computer Name Tab, See what is written in Workgroup. Change one computer by clicking on change and then type in the name of the other computer in the workgroup space down the bottom. Do not make the computer part of a domain. You want Workgroup.
This name change will require a computer reboot.
When both computers are on the same workgroup, we need to set IP Addresses.
In Control Panel, Open Network Settings.
Right click on Local Area Connections and select properties.
Under the heading "This connection uses the following items, Find Internet Protocol (TCP/IP)
Highlight it, Make sure you don't untick the box, and click on properties
Under the heading Use the following IP Address ENter in the Following on ONE Computer.
IP Address 192.168.0.10
Subnet Mask 255.255.255.0
Default Gateway LEave Blank
Under the Heading Obtain DNS Serveraddress automatically
Set this to Automatic. Don't enter anything in.
On the second computer Make the IP Address 192.168.0.20
Everything else the same.
This should be all.