function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}
addLoadEvent(function() {
	num = Math.floor(Math.random()*4)+1;
	document.getElementById("Header").style.background = "url('themes/tabled/styles/default/bg"+num+".jpg') repeat-x center top #E5EAF6";
});