Hello,
I already have the solution on my laptop.
I used the fancybox script that is in your attached files to display the popup.
Also, I used cookies for checking/unchecking the checkbox and remembering if the popup should be displayed or not.
I can help you with setup, can give any explanations.
I can also provide you an example which uses the jquery dialog (modal/popup window script) instead of the fancybox script.
I will explain how everything works in the solution and if you require changes, we can also do those.
I'm an IT professional with 8 years of experience in developing web applications.
This has been an easy & fun fix.
Kind regards,
Bogdan