Site to Site VPN routing - Cisco 1841 to Nortel VPN Router 1010

I am trying to connect a Cisco 1841 router to a Nortel VPN Router 1010 via a IPSEC VPN tunnel. I actually have the tunnel up and running. My problem is that I cannot figure out how to tell the Cisco Router to route traffic from its private network to the private network on the Nortel Router. The Nortel Router seems to just route traffic to the Cisco Router's public interface and it works. If I put a static route in the Cisco Router to route to the Nortel Router's public interface, I get nothing. Any help would be appreciated.