[CentOS] setup firewall with 3 nic cards

I am trying to setup some rules on a box with 3 nic cards. Two internet 
connections and one office connection.

eth0 is office
eth1 is internet T1
eth2 is internet Cable

when I do "iptables -F" then iptables -L everything is gone as it should be.

Then I do
iptables -t nat -A PREROUTING -p tcp -d $MYIP --dport 6550 -j DNAT --to 
$INTERNAL_ADDRESS:6550
iptables -t nat -A POSTROUTING -d $INTERNAL_ADDRESS -j SNAT --to $GWIP

then I do iptables -L again and the rule is not there. Am I missing 
something?
I have tried -I and -A both.

Thanks,

Jerry