How to use NAT in Bridge mode

[auther_bin]

Hello friends:

  I have use a firebox in my intranet and used bridge mode by patched: 
bridge-nf-0.0.6-against-2.4.17.diff, and used well on it, but I want to use NAT on 
that bridge, which used on eth0(Internet) and eth1(Intranet), I config each interface 
an IP address like: eth0:12.12.12.12    eth1:11.11.11.11. Some times, I want to NAT 
11.11.11.X to 12.12.12.12, How Can I, just use the iptables rules, It not work at all, 
and must I use some other way?

  Thanks for advices.

auther_bin