Another Internet Connection Issue

HI all Please help
I have a Windows 2003 Sever and a cable Broadband Internet connection> My problem is that when I configure my Server to static IP address I cannot browse the Internet, although when I get a DHCP address from my Modem/router I can.
The modem is plugged into a switch as is my server. I have only one Nic installed in the server and do not require Internet connection sharing. I need all of this as I am upgrading this server to AD and need static IP for DNS

Please help and Thanks