I agree with Krissovo. There is a lot of info missing. For instance, is there one computer that connects to the Internet? You said your ISP provides your connection via LAN. Did you also receive an IP address(not typical)? If so, then your machine to internet is your "router", which means you will have to use this IP address as Gateway for your clients.(see below on Gateway)
If you receive a dynamic IP address(normal) then I would assign the "Router" a static IP address i.e. 192.168.0.1(Class C Network not seen in Internet for use locally). You can set this in Network Settings under TCP/IP for the network adapter.
Does this "Router" have 2 network cards or do you have a Hardware Router installed? Also, is there a hup/switch in play here? How is it all connected?
You will also have to configure you clients. First you will assign these an IP address similiar to the above only ending the last number.
ex. 192.168.0.2 192.168.0.3 192.168.0.4 etc.
Next, you should assign the clients a DNS(Domain Name Service) name. You give them the name of the computer where they sit ie. Computer "Don" has and IP address of 192.168.0.2 etc. You will also have to assign a "DNS server". Use the router 192.168.0.1. This way, when someone wantsto FTP to a site, your router will resolve the names. By the way, you can also configure your Router as a DHCP Server(Dynamic Host Configuration Protocol). That way, you wont have to assign any IP address to the clients. They will all receive it automatically. That is if you set the clients to access DHCP Server in Network settings.
Sorry if this sounds Spanish but more info is better. Check out how you got it all hooked up. Document it and come back here. If you come back, I will go in moredetail.
Kimble
