if(screen.availHeight < 530)
{
 	document.write("<link rel=stylesheet type=text/css href=css/navigation_640.css>");
}
else
{
	if (screen.availHeight < 650)
	{
		document.write("<link rel=stylesheet type=text/css href=css/navigation_800.css>");
	}
  else
	{
  	if (screen.availHeight < 820)
		{
			document.write("<link rel=stylesheet type=text/css href=css/navigation_1024.css>");
		}
		else
		{
			document.write("<link rel=stylesheet type=text/css href=css/navigation_1280.css>");
		}
	}
}