Loop.js

var Loop = new Class({

  loopCount: 0,
  isStopped: true,
  isLooping: false,
  loopMethod: $empty,

  setLoop: function(fn, delay){
    if(this.isLooping) {
      this.stopLoop();
      var wasLooping = true;
    } else {
      var wasLooping = false;
    }
    this.loopMethod = fn;
    this.loopDelay = delay || 3000;
    if(wasLooping) this.startLoop();
    return this;
  },

  stopLoop: function() {
    this.isStopped = true;
    this.isLooping = false;
    $clear(this.periodical);
    return this;
  },

  startLoop: function(delay) {
    if(this.isStopped){
      var delay = (delay) ? delay : this.loopDelay;
      this.isStopped = false;
      this.isLooping = true;
      this.periodical = this.looper.periodical(delay,this);
    };
    return this;
  },

  resetLoop: function(){
    this.loopCount = 0;
    return this;
  },

  looper: function(){
    this.loopCount++;
    this.loopMethod(this.loopCount);
    return this;
  }

});

SpriteAnimation.js

var SpriteAnimation = new Class({

  Implements: [Options, Events, Loop],
 
    options: {
        frameWidth: 75,
        frames: 10,
        frameRate: 100,
        defaultPosition: {x: 0, y :0}
      },
  
  jQuery: 'spriteAnimation',

  initialize: function(selector, options){
    this.setOptions(options);
    this.setLoop(this.step, this.options.frameRate);
    this.element = jQuery(selector);
    var pos = this.options.defaultPosition.x + 'px ' + this.options.defaultPosition.y + 'px';
    this.element.css({'background-position': pos});
    this.startLoop();
  },

  step: function(){
    var x = this.computeX();
    var y = this.computeY();
    this.element.css({'background-position': x+'px '+ y+'px'});
    return this;
  },
  
  computeX: function(){
    this.loopCount = (this.loopCount == (this.options.frames)) ? this.options.defaultPosition.x : this.loopCount
    return -this.loopCount * this.options.frameWidth;
  },
  
  computeY: function(){
    return this.options.defaultPosition.y;
  }

});