I'm looking to hire a developer to help me build a website and I want a 'drag-and-drop window' functionality, say to order a list of items.

I really rate the functionality of www.grooveshark.com? (the planned website has nothing to do with music or anything closely to related to www.grooveshark.com?, I just rate their client interface). I believe grooveshark is built using JavaScript (and apparently some ActionScript 3?)

I'll be building the mySQL database myself, and I believe I have enough experience with php, css & html to project manage the creation from that side.

However I'm unfamiliar with JavaScript code, except bits I've hacked myself in the past. What kind of code is used to create this kind of drag-and-drop functionality?

And roughly how much time would a developer require to build something like that, per experience basis.

Thanks for any help you can give