A multihomed system has two NICs so that it can route traffic between two networks. This configuration is possible on Windows 2000 Professional systems only if you've turned on IP forwarding. In Windows NT 4.0, you enable IP forwarding by selecting the Control Panel Network applet, highlighting TCP/IP Protocol on the Protocols tab, clicking Properties, then selecting the Enable IP Forwarding check box on the Routing tab.
This tab and the Enable IP Forwarding check box have disappeared in Win2K, but the functionality still exists. To turn on IP forwarding in Win2K, use a registry editor to open the registry. Under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters subkey, change the value of the IPEnableRouter entry from 0 (the default value) to 1 (enable IP forwarding), then exit the registry.