some sites allow you to drag and drop elements arround the screen
Many ways are possible. Not all are good.
Can you post links to some examples?
If you really want to know HOW things are done, View Source in your browser.
Most likely you'll find a few script libraries like jQuery, MooTools or WordPress Plug-ins behind it.
Nancy O.Alt-Web Design & PublishingWeb | Graphics | Print | Media Specialistshttp://alt-web.com/http://twitter.com/altweb