newbie question

Hello, in my little lan i must configure a linux firewall with 3 eth cards: eth0 ( xxx.xxx.xxx.yyy ) <---> to internet router ( xxx,xxx.xxx.xxx ) eth1 ( 192.168.1.1 ) <---> to my internal lan (192.168.1.0 ) eth2 ( 192.168.2.1 ) <---> to my dmz lan ( 192.168.2.0 ) How can i set the iptables firewall for natting my dmz HTTP xxx.xxx.xxx.hhh ) and SMTP ( xxx.xxx.xxx.sss )??? I've tryed with .. ..................... iptables -t nat -A POSTROUTING -s 192.168.2.hhh -o eth0 -j SNAT --to-source xxx.xxx.xxx.hhh iptables -t nat -A PREROUTING -i eth0 -d xxx.xxx.xxx.hhh -j DNAT --to 192.168.2.hhh ..................... with no results ... I apologize for my bad english and my poor "linux know-how" Thank you in advance, Mario