I used to do that exact same thing with AT&T @home cablemodem a couple years ago. I stopped using it only because I had to use Nortel VPN and it wouldn't go through Novell's NAT.
There are a lot of things you need to do, so i'll give you some brief info that will point you in the right direction. You should be able to find information as needed on how to complete each task.
1) Need 2 NICS in the server... One for public interface, one for internal private network
2) Need to configure NAT to translate the Private address to the Public address. Do this in INETCFG under the TCP/IP bindings. You'll have toAlso enable NAT implicit filtering under PROTOCOLS ==> TCP/IP
3) Need to setup DHCPCLNT.NLM to dynamically obtain IP address from cablemodem. check here for details
4) You'll probably want to use FILTCFG.NLM to setup filters on the NICS.
5) Then you just have to connect the NIC for the internal network to a switch that is on the same subnet as your workstations.. Connect the Public NIC directly to the cablemodem.
Example config...
NIC 1: 64.56.12.125 (public Interface to cablemodem)
NIC 2: 192.168.0.1 (Private interface to internal network)
Workstation 1: 192.168.0.2
Workstation 2: 192.168.0.3
etc.
See this link for nitty gritty NAT details.
Hope that helps. Marv
Marvin Huffaker MCNE, CNE
Marvin Huffaker Consulting