function randomImage(){

  var myImage = new Array();

  myImage[1]="url(imagens/natal.jpg) 50% top no-repeat";

var ry = Math.floor( Math.random() * myImage.length );

  if (ry==0)
     ry=1;
  
	//alert(myImage[ry]);
  return myImage[ry];
}

function changecss(theClass,element,value) {
	 var cssRules;
	 if (document.all) { cssRules = 'rules'; }
	 else if (document.getElementById) { cssRules = 'cssRules'; }
	 for (var S = 0; S < document.styleSheets.length; S++){
	  for (var R = 0; R < document.styleSheets[S][cssRules].length; R++) {
	   if (document.styleSheets[S][cssRules][R].selectorText == theClass) {
	    document.styleSheets[S][cssRules][R].style[element] = value;
	   }
	  }
	 }	
}