I have a combo of 3 listboxes which I would like to repopulate ( the 2nd and the 3rd listboxes ) after the selection of the 1st listbox. I don't understand how the page should refresh itself once selected.

PHP Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
    <head>
        <title></title>
        <script language="JavaScript" type="text/javascript">
        <!--
            function go(action) {
            
            // set variables pointing to the two forms we need
            var theForm = document.forms["myForm"];
            var otherForm = window.parent.document.forms["myForm"];
            
            // construct the "search" part of the URL from all the elements
            var query = "?Book=" + theForm.Book.options[theForm.Book.selectedIndex].value;
            query += "&Chapter=" + theForm.Chapter.options[theForm.Chapter.selectedIndex].value;
            
            // test to see if a verse has been selected, if not we won't pass the values
            if( theForm.verse.selectedIndex != -1 ) {
                for( var i=0; i < theForm.verse.options.length; i++ ) {
                    if( theForm.verse.options[i].selected ) {
                        query += "&Verse=" + theForm.verse.options[i].value;
                    }
                }
            }
            
            query += "&Keyword=" + escape(otherForm.Keyword.value);
            query += "&Keywordb=" + escape(otherForm.Keywordb.value);
            query += "&Keywordc=" + escape(otherForm.Keywordc.value);
            query += "&Keywordd=" + escape(otherForm.Keywordd.value);
            query += "&Keyworde=" + escape(otherForm.Keyworde.value);
            query += "&Keywordf=" + escape(otherForm.Keywordf.value);
            query += "&";
            
            // either redirect this page or the child frame depending on which select was changed
            if(action == "refresh") {
                location.href = "showbook.php" + query;
            } else {
                ifrVerse.location.href = "showverse.php" + query;
            }
            
            }
        //-->
        </script>
    </head>
    <body>
        <table border="0" bgcolor="#FFFCDC">
            <td>
                <form name="myForm" id="myForm" action="showverse.php" method="get" target="ifrVerse">
                    <table border="0" bgcolor="#FFFCDC">
                        <tr>
                            <th align="center" color="white">
                        </tr>
                         <tr>
                             <th colspan="1" align="center">book</th>
                             <th colspan="1" align="center">chapter</th>
                         </tr>
                        <tr>
                            <td>
                                 <?php
                                     
require_once('mysql.php');
?>
                    
                    <input type="hidden" name="Keyword" value="" />
                    <input type="hidden" name="Keywordb" value="" />
                    <input type="hidden" name="Keywordc" value="" />
                    <input type="hidden" name="Keywordd" value="" />
                    <input type="hidden" name="Keyworde" value="" />
                    <input type="hidden" name="Keywordf" value="" />

<?php
                                    $result 
mysql_query("SELECT DISTINCT book_title, book FROM bible");
                                    
                                    echo 
"<a name='bcv'><select name='Book' id='Book' size='5' style='width:150px;' onChange=\"go('refresh');\"></a>"."\n";
                                    while(
$row mysql_fetch_array($result))
                                      {
                                      
                                      echo 
"<option value='" $row['book'] . "'>";
                                      echo 
$row['book_title'];
                                      echo 
"</option>"."\n";
                                      
                                      }
                                    echo 
"</select>"."\n";
?>
                            </td>
                            <td colspan="1" align="center">

<?php
                                    $book 
$_GET["Book"];
                                    
$result mysql_query("SELECT DISTINCT chapter, book FROM bible WHERE book = '" $book "'");
                                    
                                    echo 
"<select name='Chapter' id='Chapter' size='5' style='width:150px;' onChange=\"go('refresh');\">"."\n";
                                    while(
$row mysql_fetch_array($result))
                                      {
                                      
                                      echo 
"<option value='" $row['chapter'] . "'>";
                                      echo 
$row['chapter'];
                                      echo 
"</option>"."\n";
                                      
                                      }
                                    echo 
"</select>"."\n";
                                    
mysql_close($con);                                    
?>
                            </td>
                            </tr>
                            <td colspan="2" align="center">
                            </td>
                    
                    
                        </tr>
                        <tr colspan="2" align="center">
                            <th colspan="3" align="center" color="black">
                                verse
                            </th>
                        </tr>
                            <td colspan="2" align="center">
                            
                                    <select multiple name="verse" size="5" style="width:120;" onChange="go('update');"> 
                            </td>
                        <tr>
                            <td align="center" colspan="2">
                                <iframe name="ifrVerse" id="ifrVerse" src="blank.php" style="height:800px; width:250px;border:0;"></iframe>
                            </td>
                        </tr>
                    </table>
                </form>
            </td>
        </table>
    </body>
</html>