function showNav(index)
	{
		switch (index) {
			case 'one':
				document.getElementById('tab1').className="selected1" ;
				document.getElementById('tab2').className="select2" ;
				document.getElementById('tab3').className="select2" ;
				document.getElementById('tab4').className="select4" ;
				document.getElementById('top_1').style.display="block" ;
				document.getElementById('top_2').style.display="none" ;
				document.getElementById('top_3').style.display="none" ;	
				document.getElementById('top_4').style.display="none" ;				
				break;
			case 'two':
				document.getElementById('tab1').className="select1" ;
				document.getElementById('tab2').className="selected2" ;
				document.getElementById('tab3').className="select2" ;
				document.getElementById('tab4').className="select4" ;
				document.getElementById('top_1').style.display="none" ;				
				document.getElementById('top_2').style.display="block" ;
				document.getElementById('top_3').style.display="none" ;
				document.getElementById('top_4').style.display="none" ;
				break ;
			case 'three':
				document.getElementById('tab1').className="select1" ;
				document.getElementById('tab2').className="select2" ;
				document.getElementById('tab3').className="selected2" ;
				document.getElementById('tab4').className="select4" ;
				document.getElementById('top_1').style.display="none" ;
				document.getElementById('top_2').style.display="none" ;
				document.getElementById('top_3').style.display="block" ;
				document.getElementById('top_4').style.display="none" ;
				break ;
			case 'four':
				document.getElementById('tab1').className="select1" ;
				document.getElementById('tab2').className="select2" ;
				document.getElementById('tab3').className="select2" ;
				document.getElementById('tab4').className="selected4" ;
				document.getElementById('top_1').style.display="none" ;
				document.getElementById('top_2').style.display="none" ;
				document.getElementById('top_3').style.display="none" ;
				document.getElementById('top_4').style.display="block" ;
				break ;
		}
	}