function switchtabs(tab){
	var active = tab;
//	alert(active);
	document.getElementById('overview_navi').className=active +"_active";
	if ((active=='first')||(active=='col2_first')){
		document.getElementById('box_last').style.display="none";
		document.getElementById('box_second').style.display="none";
		document.getElementById('box_first').style.display="block";
	} else if ((active=='second')||(active=='col2_second')){
		document.getElementById('box_first').style.display="none";
		document.getElementById('box_last').style.display="none";
		document.getElementById('box_second').style.display="block";
	} else {
		document.getElementById('box_first').style.display="none";
		document.getElementById('box_second').style.display="none";
		document.getElementById('box_last').style.display="block";
	}
}