var imagenumber = 3 ;
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;

images = new Array
images[1] = 'http://www.wildclimb.ro/img/headers/header1.jpg'
images[2] = 'http://www.wildclimb.ro/img/headers/header2.jpg'
images[3] = 'http://www.wildclimb.ro/img/headers/header3.jpg'

var image = images[rand1]
document.write("<img src='" +image+ "' alt='WildClimb' class='header' >")