<form method="post" action="">
Username: <input type="text" name="username" value="" /><br/>
Password: <input type="password" name="pass" value="" /><br/>
Repeat Password: <input type="password" name="pass2" value=""/><br/>
<input type="submit" name="submit" value="Submit" />
</form>

<?php
$conn = mysql_connect("localhost", "root", "rob1991");
$db = mysql_select_db("coproj");

if(isset($_POST['submit']))
{
     if(isset($_POST['pass']) && $_POST['pass'] != "")
     {
          if($_POST['pass'] == $_POST['pass2'])
          {
               if(strlen($_POST['pass']) > 3 && strlen($_POST['pass']) < 32)
               {
                    $sql = "INSERT INTO `tablename` (Table1, Table2) VALUES ('".$_POST['username']."', '".$_POST['pass']."')";
                    $sql = mysql_query($sql);
                    echo "Registered Successfully";
               } else {
                    die("Your password must be between 3 and 32 characters.");
               }
          } else {
               die("Your passwords do not match.");
          }
     } else {
          die("Please enter in a password.");
     }
}
?>