redirect to a page the fist time a site is accessed

Hi, I have some code in my index.php file that check the user agent and redirects to a warning page if IE 6 or less is encountered. 1. I'm using a framework and so calls to all pages go through index.php 2. The code that checks for IE 6 or less and redirects is in index.php I know how to redirect the users but what I want to do is redirect a user ONLY the first time the web site is accessed regardless of what page they first access. I would like to minimize overhead (no database). Can this be done? Thanks, Don