Quick question here...

I have a machine with two NIC's.
One has the IP of 192.168.1.100 (LAN1 side)
One has the IP of 172.10.10.100 (LAN2 side)

The LAN1 side has a router at 192.168.1.1 for our internet connection.
The LAN2 side is just for testing (small hub with a few computers).

Up till now, the LAN2 side had been isolated from the LAN1 side, but I
would like for the LAN2 side to be able to see a specific internet IP.
For sake of example, we'll say this internet IP is 10.10.10.10. If I
were in the 192.168.1.0 network, obviously I have a gateway at
192.168.1.1 and all goes well. But how do I add a route so that LAN2
can see this single internet IP, but no others?