You can connect your PCs using any of several different kinds of gear. Most of the world's offices are wired with Ethernet cable, but all kinds of possibilities await, including networking systems that rely on the phone or power lines already in your walls, and even wireless systems that don't need cables at all. Here's an overview of the most popular networking systems.
Note:
Be sure that whatever networking gear you buy is compatible with Windows XP by checking the compatibility list at www.microsoft.com/hcl. Networking is complicated enough without having to troubleshoot some gadget that's not designed for XP.