NATTING

Dears,
I have a scenario that is somehow making me have a hardtime , i have a wiless access point that get the internat access from my linux box, i want any user that uses my internet to get a lnading page for my self ( some kind of advertisment ) and then go to the internet , i don't need authentication , but i dont want this landing page occuring many more than once for the user ... anyhow , how can i do it with iptables? i want to DNAT all users to an internal apache server , then SNAT them to the inernet , how is that possible? double natting? proxying ? i need your help ..

regards,

oozie