Some things to check:
1. All systems are part of the same workgroup
2. All systems have different computer names.
3. If using TCP/IP, assign different IPs to all systems unless using DHCP. Must be on the same Network, but different host. Ex. 192.168.1.8, 192.168.1.9 The 192.168.1 is the network part and 8 & 9 are the host part of the IP address.
4. If using Linksys, Etherfast, Cable/DSL Router, see this link for support. This router uses DHCP.
http://www.linksys.com/tech_helper/default.html
5. You will need to share something (e.g. drive, folder, printer...).
6. If some systems are running Windows NT/2000/XP, make sure it has user accounts for the Win9x/ME systems.
7. If using a firewall, make sure all systems on the network are on the trust list of your firewall software
8. Using Windows XP? Need help with file sharing?
Read this excellent article with step-by-step instructions on how to do this.
9. Even if it tells you to do it, don't run Windows XP's Network Setup Wizard on the other networked computers. You want to make the Windows XP computer conform to the existing network. The Wizard wants to make the rest of the network conform to XP.
10. You must disable Windows XP's Internet Connection Firewall (ICF) on a local area network connection to other computers. If it's enabled on a LAN, ICF will block file and printer sharing. This is probably the most common problem in Windows XP networking.
11. To make most network settings, you must be logged on as a user that is a member of the Administrators group.
12. Use the same protocol for File and Printer Sharing on all computers.