Fedora Users — firewall ??

I am getting ready to build my first firewall, using Fedora Core 2. I have read a lot of tutorials, but all of them are for firewall with NAT enabled. What do I do if I don't need NAT. For example, I have a network with 50 Class B Ip's we use a default gateway supplied by our University and DHCP to distribute the IP's. So the only thing I really need to do is firewall my 50 IP's from the outside world while continuing to use our given IP's and gateway. Any thoughts on how to set this up would be appreciated.

One more question, when connecting the outgoing NIC from the firewall to the rest of the network do I need to use a crossover cable or will I specify that the NIC is supposed to be outgoing in firewall configuration?

Thanks for the help.

Bobby K