var imagenumber = 8 ;//numero de imagens
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;
images = new Array
images[1] = "ban_good.jpg"//aqui as imagens
images[2] = "ban_musical.jpg"
images[3] = "ban_tarde.jpg"
images[4] = "ban_noite.jpg"
images[5] = "ban_almocando.jpg"
images[6] = "ban_sucessos.jpg"
images[7] = "ban_toques.jpg"
images[8] = "ban_marcacao.jpg"

var image = images[rand1]