DHCP subnet

I have a W2K3 server. The WAN is connected through a Time Warner Telecom device that run on a Class C subnet (255.255.255.0). I cannot use a dual NIC system and have the Internal LAN on the same subnet. Can I reconfigure the scope and use a subnet mask of 255.255.254.0 and expect it to work.

Keep in mind the server is already running on a single NIC with the Class C subnet. I had to set it up that way to get it to work. Is this practical to get the dual NIC arangement to work?