Note: This code has been written with WordPress 2.8 in mind. It won't work on versions prior to 2.6 and might have unpredictable results in later versions.
Drag and drop is a useful mechanism to do stuff and can turn a complicated set of buttons or drop down lists into a simple elegant solution.
Wordpress has lots of scripts built in, which do a lot of useful functions. However, they are not enabled by default, which means that in order to get your script to work you need to enable them.