Help with Dynamic Checkbox

hye all, im here just want to ask for a very basic problem about checkbox. i do search but there is nothing related to my problem.

my problem is :

1. i have a dynamic table with checkbox on each row of my table.

2. each row has different value since it carry out from my database.

3. i want to multiple add from the selected checkbox into the other table.

4. thing is fine but then, there is no value carry to the database. ( i noticed that i don carry any value into it, i dont know how to do that ).

here is the sample of my code :

//<?php
    while($rows=mysql_fetch_array($result)){
    ?>
    <tr bgcolor="#B9DAFC">
    <td align="center" class="text">
        <? echo $rows['subject_id']; ?></td>
    <td class="text">
        <? echo $rows['subject_name']; ?> </td>
    <td align="center" class="text">
    <input name="checkbox[]" type="checkbox"    id="checkbox[]" value="<? echo $rows['id']; ?>">
      </td>
    </tr>
    <?php
    }
    ?>


<tr align="right">
    <td colspan="3" bgcolor="#FFFFFF">
<input name="add" type="submit" id="add" value="Add!">
    </td>
</tr>
    <?
    if($add){
    foreach($_POST['checkbox'] as $add_id)
    {
    //for($i=0;$i<$count;$i++){
    $add_id = $checkbox[$i];    
    $sql = "INSERT INTO $tbl_name2 (subject_id, subject_name) VALUES ('$add_id', '$add_id')";
    $result = mysql_query($sql);
    }

    // if successful redirect to user.php
    if($result){
    echo "<meta http-equiv=\"refresh\" content=\"0;URL=user.php\">";
    }
    }
    mysql_close();
    ?>

thank you in advance.