var backgroundArray = new Array();
	backgroundArray[0] = "images/bg_01.jpg";
	backgroundArray[1] = "images/bg_02.jpg";
	backgroundArray[2] = "images/bg_03.jpg";
	backgroundArray[3] = "images/bg_11.jpg";

var nIndex = 0;
var timerID = null;
function rotateBackground(){
	var len = backgroundArray.length;
	if(nIndex >= len)
		nIndex = 3;
	document.getElementById('backimage').src = backgroundArray[nIndex];
	nIndex++;
	timerID = setTimeout('rotateBackground()',3000);
}