Control Panel / Network / Protocols / TCPIP properties / Advanced
Add the IPs here along with the appropriate subnet masks (e.g.
255.255.255.0) for each. After they're added, you'll need to reboot NT
(eventhough NT doesn't mention anything about it). For this reason, you
may want to put more in there than you currently need, so that when you do
need them, you won't have to reboot the machine again for a while...