rolloverClassName = 'rollover';
altKey = '_o';

if(window.addEventListener)
    window.addEventListener("load", rolloverOnload, false);
else if(window.attachEvent)
    window.attachEvent("onload", rolloverOnload);


function rolloverOnload(){
	
	var oImgs = document.getElementsByTagName('img');
	var oRolloverImgs = new Array();
	for(i = 0; i < oImgs.length; i++ ){
		if(oImgs[i].className == rolloverClassName){
			oRolloverImgs[oRolloverImgs.length] = oImgs[i];
		}
	}
	
	
	var preLoadImgs = new Array();
	for(i = 0; i < oRolloverImgs.length; i++){
		var src = oRolloverImgs[i].src;
		var pid = src.lastIndexOf('.');
		overSrc = src.substr(0,pid) + altKey + src.substr(pid);
		preLoadImgs[i] = new Image();
		preLoadImgs[i].src = overSrc;
		rollover(oRolloverImgs[i], overSrc, src);
	}
	
	function rollover(obj, over, out){
		obj.onmouseover = function(){this.src = over};
		obj.onmouseout  = function(){this.src = out};
	}

}