Esentially this is Facebox ( famspam.com/facebox ) for prototype.
It is designed to hook up to your a[rel=popupbox] tags and display whatever it is in their href in a fancy popup div.
Add in the <head> section of your page:
Now this will happen:
<a href="#terms" rel="facebox">Terms</a>
Loads the #terms div in the box
<a href="terms.html" rel="facebox">Terms</a>
Loads the terms.html page in the box
<a href="terms.png" rel="facebox">Terms</a>
Loads the terms.png image in the box
In short - do whatever you want to and be happy. I hate legal stuff but if you are into it - it is GPL. For more information goto www.gnu.org/licenses/gpl.html