....adding a bit more information to the solution, once you enable IP routing, you can manually create entries by opening a command prompt (start-->run--->cmd) and use the "route" command.
e.g
"Route print" will show you the current routing table entries
"Route add 10.0.0.1 mask 255.0.0.0 192.168.0.1" adds a entry to the routing table that tells it in order to reach host 10.0.0.1, it must use the gateway 192.168.0.1 which in most cases would be your LAN's gateway/router.
For more information, type "Route /?". You will be presented with examples and a detailed explanation of the command!
