Windows Server 2003 can do much more than just file sharing and Web site hosting. Using the Routing And Remote Access Services (RRAS) component, you can configure your WS2K3 system to act as a router. For this to work, you need to have multiple network adapters on different subnets.
To set this up, follow these steps:
In the RRAS window, right-click the server, and select Properties. On the General tab, you'll see the Enable This Computer As A Router option selected, along with the Perform LAN Routing Only option. On the IP tab, you'll see the Enable IP Routing option selected.
Depending on your network topology, you may need to reconfigure your clients to use this server as their default router.