Ipchains redirecction

Hi Guys, i have this situation I have 1 web server running IIS and is behind a firewall that runs on SuSE :) In the firewall i have running a proxy software who redirects all trafic from the port 80 to port 80 on my web server. It works fine to protect the IIS box, but the logs have only the ip number of the firewall machine. Can i with ipchains redirect the traffic as i do with the proxy software?? and if it's possible, the web server logs will capture the real ip of the visitors?? Thanks a lot !! Alfredo