Ok, well I guess that just impressed the hell out of everybody...lol.
Anyway, here is another way to do pretty much the same thing but perhaps more inline with the original question.
On this one. I have 2 divs on the main page. On the first div I have the main content for the page and on the second div I have an enter href, like a warning page would have it.
The first div is hidden at load time and the second div is not.
The href is pointed at my second page with the target opening in _blank and the self.blur at top (just like the original example). There is an onclick event which hides the second div and shows the main content.
Seems to work fine as a popunder in the 5 minutes of testing I gave it.
http://www.partyafterdark.com/poptest/firstpage1.htm