var imagenumber = 5 ;

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

images2 = new Array
images2[1] = "banners/banner.jpg"
images2[2] = "banners/banner1.jpg"
images2[3] = "banners/banner2.jpg"
images2[4] = "banners/banner3.jpg"
images2[5] = "banners/banner4.jpg"

var image2 = images2[rand1]