Combos dinamicos

[elimaira]

Hola tengo un problema.....necesito hacer 3 select dinamicos dependientes, pro yo tengo un script para hacer 2 select nada mas pro el tercero no se como crearlo...ya q tengo poco conocimientos de javascript....

Código HTML:

<form method="post" name="form_combo" action="">	
	<table width="100%" border="0" cellspacing="2" cellpadding="2" class="style2">
      <tr>
        <td width="7%">&nbsp;</td>
        <td width="20%">Areas</td>
        <td width="73%">
		<? $result_categories = mysql_query("select * from sub_linea order by nombre"); ?>
		<select name="id_category" class="stylen" onChange="redirect(this.options.selectedIndex)">
		<option value="-1">Selecione</option>
        <? while ($row_categories = mysql_fetch_array($result_categories)) { ?>
		  <option value="<? echo $row_categories["id"]; ?>">
		  <? echo $row_categories["nombre"]; ?> </option>
		  <? } ?>
        </select> </td>
        </tr>
      <tr>
        <td>&nbsp;</td>
        <td>Aplicaciones</td>
        <td>
		<? $result_subcategories = mysql_query("select * from uso,area_posee_uso where area_posee_uso.id_uso='$id_category_combo' and uso.id=area_posee_uso.id_uso"); ?>
		<select name="id_subcategory" class="stylen" onChange="redirect(this.options.selectedIndex)">
		<option value="-1">Selecione</option>
        <? while ($row_subcategories = mysql_fetch_array($result_subcategories)) { ?>
		  <option value="<? echo $row_subcategories["id"]; ?>">
		  <? echo $row_subcategories["nombre"]; ?> </option>
		  <? } ?>
        </select> </td>
        </tr>

      <tr>
        <td>&nbsp;</td>
        <td>Categorias (Lineas) </td>
        <td><? $result_lineas = mysql_query("select * from sub_linea,linea_pose_area where linea_posee_area.id_area='$id_sub_category' and linea.id=linea_posee_area.id_area"); ?>
		<select name="id_linea" class="stylen">
		<option value="-1">Selecione</option>
        <? while ($row_lineas = mysql_fetch_array($result_lineas)) { ?>
		  <option value="<? echo $row_lineas["id"]; ?>">
		  <? echo $row_lineas["nombre"]; ?> </option>
		  <? } ?>
        </select> </td>
      </tr>
      <tr>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td><input type="submit" name="Submit2" value="Enviar" class="stylen" /></td>
      </tr>
      <tr>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        </tr>
    </table>
<? $result_categories_combo = mysql_query("select * from sub_linea order by nombre"); ?>
<script>
<!--
var groups=document.form_combo.id_category.options.length
var group=new Array(groups)
for (i=0; i<groups; i++)
group[i]=new Array()

//tercer select
var groups1=document.form_combo.id_subcategory.options.length
var group1=new Array(groups1)
for (i=0; i<groups1; i++)
group1[i]=new Array()



<? $group_i = 0; ?>
<? $group_j = 1; ?>
<? 
     while ($row_categories_combo = mysql_fetch_array($result_categories_combo)) 
	 {
	        $id_category_combo = $row_categories_combo["id"]; 
?>
<?      $group_i = 0; 
?>
<?      $result_subcategories_combo = mysql_query("select * from uso,area_posee_uso where area_posee_uso.id_area='$id_category_combo' and uso.id=area_posee_uso.id_uso"); 
?>

//document.form_combo.id_subcategory.length =<? //$num = mysql_num_rows($result_subcategories_combo); echo $num;?>;

      group[0][<? echo $group_j; ?>]=new Option("<? echo $row_categories_combo["nombre"]; ?>","<? echo $row_categories_combo["id"]; ?>")
      
<? while ($row_subcategories_combo = mysql_fetch_array($result_subcategories_combo))  
     {  
?>

group[<? echo $group_j; ?>][<? echo $group_i; ?>]=new Option("<? echo $row_subcategories_combo["nombre"]; ?>","<? echo $row_subcategories_combo["id"]; ?>")

<?        $group_i++; 
       }//fin while subcategorias
 ?>

<?   $group_j++;
    } //fin while categorias
?>

var temp=document.form_combo.id_subcategory
 
function redirect(x)
{
     for (m=temp.options.length-1;m>0;m--)
          temp.options[m]=null
     for (i=0;i<group[x].length;i++)
	 {
        temp.options[i]=new Option(group[x][i].text,group[x][i].value)
     }
  temp.options[0].selected=true
}

//-->
</script>	
</form>	
</body>
</html> 

si me podrian ayudar a resolver esto por favor...es q lo necesito urgente....