function menuButtons(div) {

  var self = this; // set up object reference
  self.suffix = '_over'; // suffix for over images
  self.div = (typeof div == 'object') ? div : $(div); // get the div object
  self.images = self.div.getElementsByTagName('img'); // store the default image objects
  
  for(var i = 0; i < self.images.length; i++) {
    // over src array
    var split = self.images[i].src.split('.');
	var overSrc = '';
	
	for (var j = 0; j < split.length; j++) {
	  if (j == (split.length - 1)) {
	    overSrc += self.suffix;
	  }
	  if (j != 0) {
	    overSrc += '.';
	  }
	  overSrc += split[j];
	}
	
  // preload images
  self.images[i].rollover = new Image();
  self.images[i].rollover.src = (overSrc);
	self.images[i].defaultSrc = self.images[i].src;
    
	self.images[i].onmouseover = function() {
	  this.src = this.rollover.src;
	}
	
	self.images[i].onmouseout = function() {
	  this.src = this.defaultSrc;
	}
	
  } // end for each image
}

ev.add(window, 'load', function() { new menuButtons('menu'); });