Networking :: Iptables - Portforward To External IP And Ports?

I want to portforward client connections from an ubuntu lts server to another external server. btw i am a noob on iptables. i have tryed using the basic commands for iptables with no success. For example:iptables -A PREROUTING -t nat -i eth1 -p tcp --dport 7878 -j DNAT --to 91.23.45.67:7878iptables -A FORWARD -p tcp -i eth1 -o eth0 -d 91.23.45.67 --dport 7878 -j ACCEPTso basically i just want a rediraction for from one ip to another. Example: A client tries to connect to ip 123.45.67.89 on port 7878 and the server forwards him to ip xx.xx.xx.xx on port 7878, meaning that xx.xx.xx.xx is the actual server with services. Server with ip 123.45.67.89 is only forwarding the client to external ip... how can this be done in a simple command?