Is this normal IP traffic?
You do NOT need a NAT entry.
You just need to push your route to clients, enable IP forwarding on the server, and make sure the gateway for the server's LAN has a route to the VPN. If the server IS the router for it's lan, then you just push a route to clients and you are done =]
http://secure-computing.net/wiki/index.php/OpenVPN/Routing