var images = new Array();

images[0] = "images/headerateex.gif"; 
images[1] = "images/headerbteex.gif";
images[2] = "images/headercteex.gif"; 
images[3] = "images/headerdteex.gif";

function ShowImg() {
var number = images.length;
var increment = Math.floor(Math.random() * number);
var strTemp ='<img src="' + images[increment] + '">';
document.write(strTemp);
}

var rotate = 5000; 
var count = 0;

function RotateImg(myImage){
 myImage.src=images[count];
 count++;
 if(count==images.length){count = 0;}
 setTimeout("RotateImg(myImage)",rotate);
}