Lightbox style popup window

I would like to have a lightbox styled popup window with newsletter signup and social media links but I'm not sure how I can do this or if there is a module for this. Ideally I want it to popup on a category page, but I only want it to popup once (if the customer goes to a product and comes back I don't want it popping up each time the page loads). Any ideas on how I can achieve this??

Any ideas? I can settle for just a random popup window instead of a lightbox styled one, just don't know how to do this...

If you search the Web for something like popup on page load, there are lots of scripts available that do that.

Here's some info on adding Javascript to Zencart:

http://www.zen-cart.com/wiki/index.php/Customisation_-_Templates_-_Javascript

Just my $.02, but there aren't many things more annoying to me as a site visitor than the 'feature' you're proposing to use. Unless there's something on your site I can't live without, I'll leave for good as soon as the popup appears. Others may not mind.