function centerElement(el){
  if(document.getElementById(el)!=null) {
      document.getElementById(el).style.left = (document.getElementById(el).parentNode.offsetWidth - document.getElementById(el).offsetWidth)/2 + 'px'
  }
}

function elementsToCenter() {
    centerElement('navigation')
    centerElement('center_images')
}

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