var image = new Array(); 
number = 0;

// imageArray
image[number++] = "images/header_ski_alpin.jpg";
image[number++] = "images/header_ski_fond.jpg";
image[number++] = "images/header_snowboard.jpg";

// keep adding items here...
increment = Math.floor(Math.random() * number);
document.getElementById("MainTD").style.background = "#00144E url('"+image[increment]+"') no-repeat top left";

//document.getElementById("MainTD").style.backgroundImage="url("+image[increment]+")";
//document.write(image[increment]);