function choose_form(f) {
     if (document.getElementById('site').checked) {
	   	f.method = "post";
		f.action = "search.php";
		f.target='_self';
		f.submit();
	 }else{
		f.method = "get";
		f.action = "http://www.google.it/search";
		f.target='_blank';
		f.submit();
	 }
	}