var myWidth = 0, myHeight = 0;
if( typeof( window.innerWidth ) == 'number' ) {
//Para navegadores que no sean IE
myWidth = window.innerWidth;
myHeight = window.innerHeight;
} else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement. clientHeight ) ) {
//IE 6 o superior en modo estándares
myWidth = document.documentElement. clientWidth;
myHeight = document.documentElement. clientHeight;
}


if ( myWidth > 1030 ) {
var capa = document.getElementById( 'bg01' );
capa.style.display = "block";
}
else {
var capa2 = document.getElementById( 'bg02' );
capa2.style.display = "block";
}