function MM_goToURL() { //v3.0
  var i, args=MM_goToURL.arguments; document.MM_returnValue = false;
  for (i=0; i<(args.length-1); i+=2) eval(args[i]+".location='"+args[i+1]+"'");
}

<!--
function checkCheckBoxes() {
var obj=document.form1.productheadingID;
var valid=false;
for(i=0;i<obj.length&&!valid;i++){
if(obj[i].checked){valid=true;}}
if(!valid){alert("You must tick at least one product to compare");return false;}
else
{
document.form1.submit();
}
} 
//-->

function checkNum(obj,box)
{cCount=0
 for (i=0;i<obj.elements.length;i++)
  if ((obj.elements[i].type=='checkbox') && (obj.elements[i].checked) ) cCount+=1
 if ((box.checked) && (cCount > 5)){
  box.checked=false
  alert('You cannot compare more than five products at a time')
 }
}


function chngeImg( theIMG , theSRC, theThumb ){
	
	var thumb = eval('document.'+theThumb);
	
	document.mainimage.src=theSRC; 
	document.mainimage.alt= theIMG;
	thumb.className='gray_image';

}