We have four computers with a Belkin 54g wireless router. One computer is connected to our dsl bya cable. The other 3 are using wireless. Whenever one of the computers gets on the network, neither of the others can.

Typical wireless consumer routers have one WAN (Wide Area Network) port and four or more wired Ethernet (1000/100/10Base-T) ports and additional ports that use the routers wireless B/G or N flavour. The WAN port is intended for your cable or ADSL modem and receives its address and other configuration items from your ISP. The inside or LAN ports all receive their addresses etc from a DHCP server running in the router.

Your inside addresses are translated to the external address in the router by a feature called NAT. This allows you to have multiple devices in your home that share a single external IP address supplied by your ISP.

This is legal and technically reliable and quite commonly used.

You want to change your current configuration to the one recommended by spydersig. You should make sure to secure your network with a pre-shared key and set up WPA/WPA2 authentication using EAP.

You need to attach the Belkin 54g wireless router to the DSL/cable modem. Then have all the computers connect wirelessly to the belkin. They should then be able to get out.