var images = img_rnd.length - 1;
var max_images = 3;

var i = Math.round(images*Math.random());

for (var k = 0; k<max_images && k<=images; k++) {
	document.write('<a href="' + img_urls[i] + '" target="_blank"><IMG SRC="' + img_rnd[i] + '"  border="0"></a> &nbsp; &nbsp;');
	if (i<images) {
		i++;
	} 
	else {
		i=0;
	}
}