function isEmail(str){
	var check=/^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
	return check.test(str);
}
function check_form(form){
	if(form['name'].value==''){
		alert("You must write your name !");
		return false;
	}
	if(!isEmail(form['email'].value)){
		alert("You Must Enter Valid E-Mail Address !");
		return false;
	}
	if(form['comment'].value==''){
		alert("You must write your comments !");
		return false;
	}
}