DHTML Goodies has a post on their site including code for a folder tree with drag and drop capabilities. It is actually a pretty creative script and works very well. It also has a demo and tutorial to implement it into your own site.
It also uses AJAX for saving the file structure to the server. The documentation is simple, but I think it is enough to get the files up and running. I don’t know how many projects this will be useful in, but I know at some point it will come in handy.
The site has quite a few other tutorials that are definitely worth bookmarking.
