Make Wordpress Theme Open New Window Via onclick= On First Click Of Slideshow Buttonn

Hey, I run viral websites which run gallery style slideshows, so basically one wordpress article with 20 or so pages so you view the first page, click Next get sent to the 2nd page and so on. And I want to make it so that when a user clicks the Next button on the very first page of the slideshow it goes to the next page, but then also opens up a new tab which directs to another link on my site at the same time. And I want it to only work on the first page of the article (don't want each time they click on the Next button the new tab to open up). So if they are at say [login to view URL] when they click the Next button they go to the next page in the slideshow along with opening the new tab up, but once they are at [login to view URL] or any other page, it just goes to the next page of the slideshow and does not open up the new tab. I have an example of another site doing this that I can provide for you.