function addListener ( elem, eventType, func, cap ) {
 if ( elem.addEventListener ) {
  elem.addEventListener ( eventType, func, cap );
 } else if ( elem.attachEvent ) {
  elem.attachEvent ( 'on' + eventType, func );
 } else {
  alert( 'A browser used is not supported.');
  return false;
 }
}


function setListeners ( e ) {


 var hn_top = document.getElementById( 'hn_top' );
 addListener ( hn_top, 'mouseover', swap_image_on,  false );
 addListener ( hn_top, 'mouseout',  swap_image_off, false );

 var hn_product = document.getElementById( 'hn_product' );
 addListener ( hn_product, 'mouseover', swap_image_on,  false );
 addListener ( hn_product, 'mouseout',  swap_image_off, false );

 var hn_company = document.getElementById( 'hn_company' );
 addListener ( hn_company, 'mouseover', swap_image_on,  false );
 addListener ( hn_company, 'mouseout',  swap_image_off, false );

 var hn_calibrate = document.getElementById( 'hn_calibrate' );
 addListener ( hn_calibrate, 'mouseover', swap_image_on,  false );
 addListener ( hn_calibrate, 'mouseout',  swap_image_off, false );

 var pl_select = document.getElementById( 'pl_select' );
 addListener ( pl_select, 'change', pulldownmenu, false );

}


addListener ( window, 'load', setListeners, false );