Do you know any html & javascript pop up window code that works fine with Pressero?

If you want to use javascript just on the home page, this is not possible. The only places where javascript can be entered without being stripped out by the system are in the Share Script area and HTML Head Content areas of Site > Settings > "SEO / HTML" tab. These areas both affect all pages in the site. There is not a way to add javascript to one page only.

However, if you would like to change the look of their home page to display some additional information, you may wish to consider making a custom page and then setting that as their home page.