function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload();
      func();
    }
  }
}


function getElementsByClass(searchClass,node,tag) {
	var classElements = new Array();
	if ( node == null )
		node = document;
	if ( tag == null )
		tag = '*';
	var els = node.getElementsByTagName(tag);
	var elsLen = els.length;
	var pattern = new RegExp('(^|\\s)'+searchClass+'(\\s|$)');
	for (i = 0, j = 0; i < elsLen; i++) {
		if ( pattern.test(els[i].className) ) {
			classElements[j] = els[i];
			j++;
		}
	}
	return classElements;
}

function roll(o)
{
var src,ftype,newsrc;
// get the src of the image, and find out the file extension
src = o.src;
ftype = src.substring(src.lastIndexOf('.'), src.length);
// check if the src already has an _on and delete it, if that is the case
if(/_on/.test(src))
{
newsrc = src.replace('_on','');
}else{
// else, add the _on to the src
newsrc = src.replace(ftype, '_on'+ftype);
}
o.src=newsrc;
}


function crear_rollover() {
	 if (!document.getElementsByTagName || !document.getElementById ) return false;
	 
	var myEls = getElementsByClass('rollover');
	var link;
	var imagenes;
	
	
	
	for ( i=0;i<myEls.length;i++ )
	{
		myEls[i].onmouseover = function () {
			roll(this);
		}
			 
		myEls[i].onmouseout = function () {
			roll(this);
		}
	}
	
}

addLoadEvent(crear_rollover);