if(screen.width==800){
	document.body.style.background="url('img/indexbg-800.gif')" ;
}
else if(screen.width==1152){
	document.body.style.background="url('img/indexbg-1152.gif')" ;
}
else if(screen.width==1280){
	document.body.style.background="url('img/indexbg-1280.gif')" ;
}
else if(screen.width==1024){
	document.body.style.background="url('img/indexbg-1024.gif')" ;
}