Debian Configuration :: Lenny Not Loading Iptables Rules

I'm having some trouble with the configuration of the iptables. I want to setup a network server to serve as Fail Over (for my 2 ISPs), DHCP and DNS. I have 3 network cards, 2 connected to ISP's routers and 1 that serves as UPLINK for my switch.

I want to add some Iptables rules so I can achieve what I want to do. The problem is that the rules I try to use, they have to effect.... they don't load, here are the rules I am trying to add:

#iptables --table nat --append POSTROUTING --out-interface eth1 -j MASQUERADE
#iptables --table nat --append POSTROUTING --out-interface eth2 -j MASQUERADE
#iptables --table nat --append POSTROUTING --out-interface eth2 -j SNAT --to EXTIP

When I try to check to see if it loads, with the command:

#iptables -L

It returns empty