window.onload = function(){
var imgTag = $$(".rollover img");
for (var i=0; i<imgTag.length; i++){
imgTag[i].onmouseover = function(){
this.src = this.src.replace(/(\.gif|\.jpg|\.png)/ , "_over"+"$1");
}
imgTag[i].onmouseout = function(){
this.src = this.src.replace(/_over/ , "");
}
}
}