Guys, if you know the way to solve this problem, please help me

I am building a testing environment for ISA Server.
The ISA Server has 2 network adapters. One adapter has IP address of 192.168.1.5, and the other has IP address of 192.168.123.5. The interface 192.168.123.5 is connected to the router that has internet connection. While, the interface 192.168.1.5 is connected to a switch that has another computer (192.168.1.6) connected.
The problem is: how can I do the routing between the interface 192.168.123.5 to the interface 192.168.1.5, and from that make the network 192.168.1.0 connect to the internet through the interface 192.168.123.5
I tried to set "ROUTE" relationship between the 2 network 192.168.1.0 and 192.168.123.0, but simply it can't work.
Many thanks