hmmm if you want just a simple twitch/jittery (but not so intense) i'd do what fxnurbs says and do just some simple expressions on the x and y values of a move2D node.
if you dont know expressions, i'd say go to the macros section of this site and I actually have a macro pack you can download (wcp macro pack 1). it has a pretty basic one called "flickrSlide" that gives you a random xy movement effect, but it is also adjustable. just ramp up the speed slider (inverted slider due to script expression mistake i made then), and it will slow the speed of the movements.