Get dynamically generated textarea value on button submit in php

<?php
    $sql = 'SELECT * from newsmanagement order by dt desc';
    $ret=mysql_query($sql) or die(mysql_error());
    while($a=mysql_fetch_assoc($ret))
    {
    ?>
        <frame id="frame <?php echo $a; ?>">
        <form action="postcomment.php?bid=<?php echo $a[newsid]; ?>& txt=tid<?php echo $a[newsid]; ?>" method="post" onsubmit="return validate(this)" enctype="multipart/form-data">
        <table class="news-content" border="0" cellspacing="2" cellpadding="0">
            <tr class="headline">
                <th>
                 <?php echo $a[headline]; ?>
                </th>
            </tr>
            <tr class="summary">
                <td>
                <?php  echo $a[summary];  ?>
                </td>
            </tr>
            <tr class="postedby">
                <td style="text-align:right" height="auto">
                <b>Posted By:</b>
                <?php echo $a[postedby];?>
                </td>
            </tr>
            <?php
            // filter comments according to the Admin approval
            $sql_inner = "select comments from newscomments where newsid='$a[newsid]' and approved ='Activate'";
            $ret_inner=mysql_query($sql_inner) or die(mysql_error());
            while($b=mysql_fetch_assoc($ret_inner))
            {
            ?>
            <tr class="comment">
                <td style="text-align:left" height="auto">
                <b>Comments:</b>
                <?php echo $b[comments]; ?>
                <br>
                </td>
            </tr>
            <?php
            }
            ?>
            <tr>
                <td><div><b>Post Comments</b></div>
                    <textarea style="width:70%; " id="tid<?php echo $a[newsid] ?>" name="tid<?php echo $a[newsid] ?>"  rows="1" ></textarea>
                    <div><input class="btn" type="submit" id="<?php echo $a[newsid] ?>" name="Comments" value="Comments" ></div>
                </td>
            </tr>
        </table>
        <div class="seperator"></div>
        </form>
        </frame>
        <?php
        }
        ?>

$newsid= $_GET['bid'];
$comment= $_GET['txt'];
if($_POST[$comment] !='')
{
    $query = "insert into newscomments(dt,comments,newsid) values(SYSDATE(),'$_POST[$comment]',$newsid)";
    if(mysql_query($query))
    {
    ?>
        <script language="javascript" type="text/javascript">
        alert("You have successfully submitted the comments");
        location.href = "home.php";
        </script>
        <?php
    }
    else
    {
        ?>
        <script language="javascript" type="text/javascript">
        alert("Error on submit comment..!");
        location.href = "home.php";
        </script>
        <?php
    }
}