var pic1= new Image(); 
pic1.src="img/left_menu/bg_red.gif"; 

var pic2= new Image(); 
pic2.src="img/left_menu/bg_grey.gif"; 

function on(x)
	{
		document.getElementById(x).style.backgroundImage="url('"+pic1.src+"')";
		
	}
function out(x)
	{
		document.getElementById(x).style.backgroundImage="url('"+pic2.src+"')";
	}