var imagenumber = 9 ;
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;
images = new Array
images[1] = "images/header_1.jpg" 
images[2] = "images/header_2.jpg" 
images[3] = "images/header_3.jpg" 
images[4] = "images/header_4.jpg"
images[5] = "images/header_5.jpg"
images[6] = "images/header_6.jpg"
images[7] = "images/header_7.jpg"
images[8] = "images/header_8.jpg"
images[9] = "images/header_9.jpg"
var image = images[rand1]