Originally Posted by Stephen

Here's one method I just implemented:

use CSS to specify div visibility: 1 div for warning, 1 for content

use a cookie + conditional switch to decide if warning should be shown:

if warning required (no cookie set, surfer from country x) show warning, then set cookie when surfer clicks "enter" > then cookie state decides whether or not to show the warning on revisit / reload. Set a session cookie that expires on browser close.

I use jQuery to keep process smooth, animated and without page refresh.

It is an interesting path to pursue and Google is your friend