function random_number()
{
    var rannum= Math.floor(Math.random()*5);
    return rannum;
}

var image=random_number();
var image_choice=new Array(5)
     image_choice[0]="<link rel=\'stylesheet\' type=\'text/css\' media=\'all\' href=\'includes/splashback-1.css\' />";
     image_choice[1]="<link rel=\'stylesheet\' type=\'text/css\' media=\'all\' href=\'includes/splashback-2.css\' />";
     image_choice[2]="<link rel=\'stylesheet\' type=\'text/css\' media=\'all\' href=\'includes/splashback-3.css\' />";  
     image_choice[3]="<link rel=\'stylesheet\' type=\'text/css\' media=\'all\' href=\'includes/splashback-4.css\' />";
     image_choice[4]="<link rel=\'stylesheet\' type=\'text/css\' media=\'all\' href=\'includes/splashback-5.css\' />";

document.write(image_choice[image]);