var ic = 6; // Number of alternative images 
var image = new Array(ic); // Array to hold filenames 
image[0] = "b1";
image[1] = "b2";
image[2] = "b3";
image[3] = "b4";
image[4] = "b5";
image[5] = "b6";

function pickRandom(range) { 
	if (Math.random) 
		return Math.round(Math.random() * (range-1)); 
	else { 
		var now = new Date(); 
		return (now.getTime() / 1000) % range;
	}
}
// Write out an IMG tag, using a randomly-chosen image name. 
var choice = pickRandom(ic); // --> 

document.writeln('<div id="banner" class="'+image[choice]+'" >&nbsp;</div>');