I'm trying to get my head around this but I think I need a point in the right direction.
I have a Cisco 1841 router which handles LAN clients and VPN clients with its own public IP address. I have another Cisco device which has it's own public IP addess as well which handles another set of local resources.
I'm not sure what the correct terminology or methodolgy for linking the subnets as the current issue is that clients behind the second Cisco device are not reachable by VPN/LAN clients.
I'm happy to provide further information when asked.