Rodrigo's code

gistfile1.js

var MySliderClass = new Class({
  
  Implements: Chain,
  
  initialize: function (element)
  {
    this.element = $(element);
  },
  
  prepareSlide: function(prop, pos0, pos1)
  {
    this.element.set('tween', {
      duration : 1000,
      transition : Fx.Transitions.Cubic.easeInOut,
      onComplete: this.slide.bind(this) // at the end of the animation call the slide method
    });
    
    // add this to the chain
    this.chain(function() {
      // need to bind this, use closures to call the tween w/ the right properties
      this.element.tween(prop, [pos0, pos1]);
    }.bind(this));
  },
  
  slide: function()
  {
    // kick of the chain
    this.callChain();
  }
  
});

var mySlider;
function init()
{
  mySlider = new MySliderClass($('quad'));
  
  // prepare the sliding animations
  mySlider.prepareSlide('left', 0, 400);
  mySlider.prepareSlide('top', 0, 200);
  mySlider.prepareSlide('left', 400, 0);
  mySlider.prepareSlide('top', 200, 0);

  // start
  mySlider.slide();
}

window.addEvent('domready', init);