No te entiendo al 100%, aca el efectp hover del background, pero no al 100%
Código HTML:
Ver original<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="es"> body {margin:0; padding:0; border:0;}
#contenedor {width:100%; height:100%; background:url('111.jpg') no-repeat center center;}
#cosas {width:500px; height:400px; margin:0 auto; background:transparent;}
body:hover>#contenedor {background:url('222.jpg') no-repeat center center;}