Well it would help if you specified an OS - Windows 95/98/2000/XP? Mac OS? Linux?
Here's how to do it in XP
Right-click My Network Places and choose properties
Locate your network cars in the list, right-click and choose properties.
Click on Internet Protocol (TCP/IP) and clisk the Properties button.
Check the option "Use the following address"
Fill in the IP address and subnet mask.
The address is not particularly important, but if you have only two machines you might use 190.168.58.1 for one and change the last number to .2 for the other.
Set the subnet mask to 256.256.256.0
Ok everything in sight and restart the machines