PHP Beginner: adding a new member to a table

Hello.  I just started learning PHP.  I'm also not very good at programming :(

I want to add a new member to a table in my database.  The table is set up so that the person_id is an automatically incremented number (so with each new member added, the person_id is +1 from the previous person_id).  I don't know how to add the information I pull off a form from a webpage to the database.  I keep getting an error telling me that it's unable to insert into the database.  Everything I have is set up on localhost using Windows XP IIS 5.0 and MySQL Server.  I made a screencap of the ER-diagram I drew of my database.  I'm only using the member and person tables for now (I think): http://img105.imageshack.us/img105/2056/db1do.jpg.  Please let me know what I did wrong, or if you need more information.  Thank you.

Partial coding:
-----------------------------------------------------------

...
  if ($isPostback) {
        $username = getRequestValue("username");
        $password = getRequestValue("password");
        $firstname = getRequestValue("firstname");
        $middlename = getRequestValue("middlename");
        $lastname = getRequestValue("lastname");
        $employer = getRequestValue("employer");
        $graduation_date = getRequestValue("graduation_date");
        $subnewsletter = getRequestValue("subnewsletter");

            $validated = true;

            if ($validated) {
              // $staff_id = $_SESSION["LoggedOnPersonId"];
          $sql = "INSERT INTO person (NULL, username, password, firstname, middlename, lastname) VALUES ";

// person_id is supposed to be on auto-increment

              $sql = $sql."('NULL', '$username', '$password', '$firstname', '$middlename', '$lastname')";

          $sql = "INSERT INTO member (employer, NULL, graduation_date, NULL, subnewsletter, firstname, middlename, lastname, NULL,) VALUES ";

// person_id is supposed to be on auto-increment

              $sql = $sql."('$employer', 'NULL', '$graduation_date', 'NULL', '$subnewsletter', '$firstname', '$middlename', '$lastname', 'NULL', )";

              //echo($sql);
                  $conn = getConnection();
                  if (mysql_query($sql, $conn)) {
                    $feedback = "Activity inserted into database successfully.";
                  }
                  else {
                    $feedback = "Error, unable to insert record into database.";
                  }
            }
            else {
              $feedback = "Invalide input.";
            }
      }
?>

...
        <form name="form1" method="post">
          <p><strong>Member Entry Form </strong></p>

            <table border="0">
            <!-- This gathers information for the person table. -->
          <tr>
            <th>UserName:</th>
            <td><input name="username" id="username"><?php echo(getRequestValue("username"))?></td>
          </tr>
          <tr>
            <th>Password:</th>
            <td><input name="password" id="password"><?php echo(getRequestValue("password"))?></td>
          </tr>
          <tr>
                <th>First Name:</th>
                <td><input name="firstname" id="firstname"><?php echo(getRequestValue("firstname"))?></td>
          </tr>
          <tr>
                <th>Middle Name:</th>
                <td><input name="middlename" id="middlename"><?php echo(getRequestValue("middlename"))?></td>
          </tr>
          <tr>
                <th>Last Name:</th>
                <td><input name="lastname" id="lastname"><?php echo(getRequestValue("lastname"))?></td>
          </tr>
          <tr>
                <th>Employer:</th>
                <td><input name="employer" id="employer"><?php echo(getRequestValue("employer"))?></td>
          </tr>
          <tr>
                <th>Graduation Date:</th>
                <td><input name="graduation_date" id="graduation_date"><?php echo(getRequestValue("graduation_date"))?></td>
          </tr>
          <tr>
                <th>Subscribe Newsletter:</th>
                <td><input name="subnewsletter" id="subnewsletter"><?php echo(getRequestValue("subnewsletter"))?></td>
          </tr>
        </table>
          <br>
          <input type="submit" name="Submit" value="Submit">
          <input type="reset" name="Submit2" value="Clear">
          <p align="center">&nbsp;</p>
        </form>
...