everything u need to know for a pop-up script
I found this thread that has scripts for a pop-up. It's A VERY LONG thread. If you read through it all, you will see that almost every question anyone's ever asked about a pop-up script is there. U can get a script that pops up once a month and only when visitors leave your site...not your page.
The only downside of this is that the thread is at another site. I understand if the moderators want to remove my post b/c it will be leaving traffic to a competitor. I just found the thread to be SO INFORMATIVE AND USEFUL and I thought others might like it too since it helped me out! I'm not trying to advertise for the site. I think SitePoint's the best! There's just been a lot of questions about pop-up scripts.