There are a few ways you can create a wireless network. If you have two or three computers, you can put a USRobotics wireless card (or a Wireless USB Adapter) in each computer to create a simple network. You will be able to share your Internet connection and also run a firewall on one of the computers. (Note: Some other companies' wireless cards will require you to purchase a standalone Access Point, even if you have only two or three computers in your network.)
How do I connect more than three computers?