Redirect http request ONCE without authentication

[Craig Russell <craig@airdigitalnetwork.com>]

I've found quite a few relatively complex solutions but I'm looking for 
something a little simpler.  I need a method of redirecting HTTP traffic 
from a specific subnet to a splash page but, only ONCE.  Once the user 
is redirected, at least initially, they will be given a splash page with 
an OK button and then they can go about their merry way.  Anyone have a 
simple way of making this happen? 

What I'm hoping for is an iptables redirect rule that will track which 
addresses have hit the rule and ignore them from then on.

Thanks for any suggestions.

Craig Russell
WDA, LLC