var EmailCheck = new RegExp("^[A-z0-9\._%-]+@([A-z0-9-]+\.)+[A-z]{2,4}$", "i");

function CheckForm(form) {
// обязательны только 2 поля - имя и адрес эл.почты

	if (form.firstname.value == "") {
		 window.alert("Please, enter your First name!")
		form.firstname.focus();
		return false;
	}

	if (form.emailaddress.value == "" || !EmailCheck.test(form.emailaddress.value)) {
		 window.alert("Please, enter valid E-mail address!");
		 form.emailaddress.focus();
		 return false;
	}
	
	if (r = document.getElementById('from_site_select') ) {
		if (r.value=="") {
			window.alert("Please, enter site!");
		 	form.from_site.focus();
		 	return false;
		}
	}
	
	return true;
 }