<?php 
require("db-connect.php");
$slt ="SELECT * FROM assingment2 ORDER BY user_id asc";
$qry =mysql_query($slt);

?>
<html>
<head><title> </title>

<script language="javascript" type="text/javascript">

 function setcourse()
 {
  var index_name=document.frmselect.name.selectedIndex;
  document.frmselect.course.selectedIndex=index_name;
 }
</script>

</head>
<body>
<form name="frmselect" id="frmselect" action="" method="post">
<table align="center">
<tr>
<td><b>NAME</b></td><td>
        <?php
            while($ftch =mysql_fetch_array($qry))
            {  
                echo'<select  name="name" id='.$ftch['user_id'].' onChange="javascript:return setcourse();">';
                echo '<option value="'.$ftch['user_id'].'">'.$ftch['name'].'</option>';

            } 
        ?>
    </select>
</td>
</tr>
<tr>
</td>
<td><b>COURSES</b></td>
<td>
        <?php
         $select="SELECT * FROM assingment3 WHERE user_id=".$ftch['user_id'];
         $execute=mysql_query($select);
            echo'<select name="course" id="course" >';
            while($fetch=mysql_fetch_array($execute))
            {
             echo '<option value="'.$fetch['id'].'">'.$fetch['courses'].'</option>';
            }
        ?>
    </select>
</td>
</tr>
</table>
</form>
<body>
<html>

/*
how will the value of second list box come and how $ftch['user_id'] this put in where condition for selcting data from table with where conditioin pls tell me*/

Post your code on (code)
This is for code and we can undertand more your problem.