function customise_popup(theForm){

 var thesize = theForm.itemSize.value;
 var prodID = theForm.itemID.value;

 if (thesize==""){

  alert("Please select a size");

 }else{

  alert(prodID + ' and size ' + thesize);

  var popURL = "customise.php?prodID="+prodID+"&size="+thesize;

  var prodPop = window.open(popURL, 'product', 'toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,xresizable=0,width=570,height=590,left = 200,top = 200');

  prodPop.focus();

 }

}