Go to the Project page and see jsPop in action.
jsPop is a javascript tool based on jQuery that provides overlayed boxes ( pop-ups ) to load contents on it.
I wrote this tool because the tools I knew to display overlayed pop-ups were focused on image gallery, like Colorbox or fancyBox do.
jsPop is focused on providing those overlayed pop-ups without the fancy stuff of an image gallery. It's a raw pop-up with no additional UI elements so you don't have to spend time removing the features you don't need of a gallery navigator.
jsPop may be useful for you if you intend to load and display html contents via AJAX or hidden HTML tags, in an overlayed pop-up.