How is your server connected to the internet. ?

what you need to do to share your internet connection is do it this way

you should have a modem, which connects to the internet. then the modem is connected to a router. your router is the connected to your server. your server should then be connected to either a switch/router which should then be connected out to all the remainig computers.

what it looks like here is that you may be missing the router between your server and the modem.

what your modem sees is the server, gives that an ip address and thats all you are entitled to.
with the modem connected to a router and then to the server. the modem sees the router and gives that the allocated ip address. the router the connects to the server with a different ip address.
so, your router will have 2 ip addresses the one that your internet service provider sees and the one that is on the local network that your server sees. this is what is called your local gateway.

this will explain some of what i have tried to explain.
http://www.ehow.com/topic_1841_computer-networking-tutorial.­html