Rails - May 2006 - Dropped Position on a Page when using a draggable element

I am playing with droppable elements and rjs.

I have a simple question. I have setup my whole page as been able to 
receive events when an object is dropped on it. It works.

Anyone knows:
- How to get the coordinates on the page the object was dropped? so for 
example I can update a database in the backend.
- How to force on display an object to be displayed at a certain 
position on a page?

any help would be very helpful.
Stephane