FxTetris = new Fx.Tween('tetris', {
	property: 'margin-top',
	duration: 10, 
	transition: Fx.Transitions.Quart.easeInOut,
	link: 'chain'
});
FxDownload = new Fx.Tween('download', {
	property: 'margin-top',
	duration: 10, 
	transition: Fx.Transitions.Quart.easeInOut,
	link: 'chain'
});
/*	now we have an fx object, let's play with it:	*/


$('btn_tetris').addEvent('mouseover', function() {
	FxTetris.start(0,10).start(10,0).start(0,10).start(10,0).start(0,10).start(10,0);
});
$('btn_download').addEvent('mouseover', function() {
	FxDownload.start(0,10).start(10,0).start(0,10).start(10,0).start(0,10).start(10,0);
});