var banner= new Array()
banner[0]="http://www.devgroupcolombia.com/images/carrusel/header.jpg"
banner[1]="http://www.devgroupcolombia.com/images/carrusel/header2.jpg"
banner[2]="http://www.devgroupcolombia.com/images/carrusel/header3.jpg"
var random=Math.floor(3*Math.random());
document.write("<style>");
document.write(".imagenes {");
document.write(' background: #000000 url("' + banner[random] 
+ '") no-repeat center top;');
document.write(" }");
document.write("</style>");