How to create an automatic popup box?

My company is having a subscription drive for a limited time and, coupled with a strong promotional push (mostly happening on radio), I expect some traffic to our website during the next few months. I'd like to create one of those boxes that appear when you come to a website to let the visitor know how they can subscribe and provide a link to our subscription page. Is there a way to integrate that into a XARA website? I know some services like AWeber have the function but I am wondering if it's possible natively. If not, is anyone using a service you like that accomplishes this?

Thanks in advance.

This way does not use any code.

In your design, create your subscription page, if it does not exist at present.
Copy your index page and for the copy, change its filename to home.
On your index page, add your subscription box with Accept and decline buttons.
The accept goes to the subscription page, the decline goes to your home page.
You may need to change all NavBars that refer to the index page to point to "home".

To revert to the original, delete the home page and on the index page, delete the subscription box. Reset the NavBar.

Acorn