function switch_vtabs(vtab) {
	var vtabs = document.getElementById('vtabs').getElementsByTagName('li').length;
	//switch off all tabs and content
	for (i=0; i < vtabs; i++) {
		document.getElementById('vtab'+(i+1)).className = '';
		document.getElementById('vtab'+(i+1)+'_content').style.display = 'none';
	}
	//switch on the selected tab and content
	document.getElementById(vtab).className = 'selected';
	document.getElementById(vtab+'_content').style.display = 'block';
}