Form Builder

Hello,

I have a site that provides webmasters with a free form for their website. Instead of a tutorial teaching them form HTML, I want to allow them to create their form with a form builder.

I want to build something like the form builder on http://www.jotform.com/

My question is, where do I start? Are there any tutorials on Internet about this? Is this really made with Javascript alone? I would really appreciate it if you guys can point me in the right direction.