<?php
$today = date("Y-m-d");
$dbh = new PDO('mysql:host=localhost;dbname=test', 'dbAdmin', '#######');
$stmt = $dbh->prepare("insert into TestGuest(Name, Date, Comment) values (?,?,?)");
$stmt->bindParam(1, $Name);
$stmt->bindParam(2, $today); /* Change here */
$stmt->bindParam(3, $Comment)...