I am running a network with 14 computers (all have win98 se) and one computer being the gateway to the net has a cable modem connection. The problem is that the clients are unable to use the net If I use NAT on the gateway which is ICS, Wingates, Nat32, Solid share, etc. But using a proxy server gives the clients access. I tried changing the IP addresses, of all the machines from 10.0.0.x to 192.168.0.x, but it still did not work. Any ideas / suggestions.
Your problem is clearly the 'Gateway' machine which is running the various internet sharing services.
The reason your internal clients can access the web via the proxy is because the proxy sends the request on behalf of the internal clinets, where as with NAT, the IP addresses are translated into public ones and sent to the Internet.
You should try to uninstall all possible ICS programs on the gateway and then install one only. If this doesn't help then you can try to update Internet Explorer, which will also update a number of other critical system files and hopefully fix the problem.