OK to network computers together you will need a NIC (network Card) in each computer, you will need a hub, switch, or router, the hub will be the cheapest. Then of course you will need the cat 5 cable.

As far as telling you how to do it I need your OS. If your using XP then you can use the networking wizard built in, I believe WIN 98 has one to. Let me know your OS, and I'll get back to you.

Also check out the microsoft support website. They might have some info to help you there.
www.support.microsoft.com