iptables -A FORWARD -p tcp -i eth0 -o eth1 -d 192.168.x.y --dport 80 -j ACCEPT
iptables -A FORWARD -p tcp -i eth0 -o eth1 -d 192.168.z.w --dport 23 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp -d tuoippubblico --dport 80 -j DNAT --to 192.168.x.y:80
iptables -t nat -A PREROUTING -p tcp -d tuoippubblico --dport 23 -j DNAT --to 192.168.z.w:23

192.168.x.y ip privato del tuo webserver
192.168.z.w ip privato del tuo server telnet