if(screen.width>=1024){ //se for 1024x768
	document.body.style.overflowX="hidden";
}
else{
	document.body.style.paddingLeft=0;
	document.body.style.backgroundImage='url("imagens/fundo800x600.jpg")';
	document.body.style.backgroundPosition='left top';
	document.getElementsByTagName("HTML")[0].style.backgroundImage = 'url("imagens/background800x600.jpg")';
}