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If your network uses cabling (or both cabling and wireless)

• First, connect the network together by running ethernet patch cables from each computer to the hub (or router or gateway device) and plug the cables into the ethernet sockets on each device. When the hub's power supply is switched on and the computers are booted-up, the green connectivity lights, top-left of each socket will light up.
• Second, check that the router or gateway device (or, if you're using a hub, one of the computers or your cable modem or ADSL/DSL router) has been set-up as a DHCP server to provide IP addresses to the other compters on the network
• Thirdly, double click on the 'My Network Places' icon in Windows XP or 2000 or the 'Network' icon in Windows Vista. The computer you're using and others in the network should be visible in the 'My Network Places' window that opens. If not, click the 'Search' button on the toolbar and enter the name of the computer(s) that can't be seen.

• Fourthly, check that you've set the Windows File and Print Sharing options to allow the sharing you intend (SortedPC recommends minimising the access rights you grant on files on your PC). Windows File and Print Sharing is part of the suite of Microsoft networking technologies. It allows computers on a network to access and use directories, files and printers located on another machine.
  Howto: XP, Vista | Download a Microsoft guide to file and printer sharing for earlier versions of Windows (2000, ME, 98 and 95).