Draggable links. (Differenciate drag and click).

hi, i've used jquery ui to make the trigger of a overlay(made with
jquerytools) draggable, but now when i drag the trigger the overlay
always open. there's a way to make overlay open only when the trigger
is clicked but not dragged?
http://www.offumac.com/
(i'm really sorry for my bad english :( )
--