var imagenumber = 4 ;

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

images2 = new Array
images2[1] = "banners/1.gif"
images2[2] = "banners/2.gif"
images2[3] = "banners/3.gif"
images2[4] = "banners/4.gif"

var image2 = images2[rand1]