part of index page
Code:
  
      <form id="form1"  name="form1" method="get" action="show.php">
        <select id="mark" name="mark">
          <option value="">--</option>
          <option value="100">BMW</option>
          <option value="101">Audi</option>
        </select>
        <select id="series" name="series">
          <option value="">--</option>          
          <option value="1" class="100">1 series</option>
          <option value="3" class="100">3 series</option>
          <option value="5" class="100">5 series</option>
          <option value="6" class="100">6 series</option>
          <option value="7" class="100">7 series</option>
          
          <option value="11" class="101">A1</option>
          <option value="23" class="101">A3</option>
          <option value="33" class="101">S3</option>
          <option value="44" class="101">A4</option>
          <option value="54" class="101">S4</option>
          
        </select>
        
		 <button name="" type="submit" > Find! </button> 
              </p>
	     
      </form>    
    

  <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js" type="text/javascript" charset="utf-8"></script>
  <script src="js/jquery.chained.js" type="text/javascript" charset="utf-8"></script> 
  <script type="text/javascript" charset="utf-8">
  $(function() {       
    $("#series").chained("#mark");
    
  });
  </script>
js
Code:
(function($) {

    $.fn.chained = function(parent_selector, options) { 
        
        return this.each(function() {
            
            /* Save this to self because this changes when scope changes. */            
            var self   = this;
            var backup = $(self).clone();
                        
            /* Handles maximum two parents now. */
            $(parent_selector).each(function() {
                                                
                $(this).bind("change", function() {
                    $(self).html(backup.html());

                    
                    var selected = "";
                    
                    selected = selected.substr(1);

                    /* Also check for first parent without subclassing. */
                    /* TODO: This should be dynamic and check for each parent */
                    /*       without subclassing. */
                    var first = $(parent_selector).first();
                    var selected_first = $(":selected", first).val();
                
                    $("option", self).each(function() {
                        /* Remove unneeded items but save the default value. */
                        if (!$(this).hasClass(selected) && 
                            !$(this).hasClass(selected_first) && $(this).val() !== "") {
                                $(this).remove();
                        }                        
                    });
                
                    /* If we have only the default value disable select. */
                    if (1 == $("option", self).size() && $(self).val() === "") {
                        $(self).attr("disabled", "disabled");
                    } else {
                        $(self).removeAttr("disabled");
                    }
                    $(self).trigger("change");
                });
                
                /* Force IE to see something selected on first page load. */
                $("option", this).first().attr("selected", "selected");
                
                /* Force updating the children. */
                $(this).trigger("change");             

            });
        });
    };
    
    /* Alias for those who like to use more English like syntax. */
    $.fn.chainedTo = $.fn.chained;
    
})(jQuery);
show.php
Code:
<?php 
if (isset($_GET['mark']))
	{
	$papar_car=$_GET['mark'];
	
	}	
if (isset($_GET['series']))
	{
	$papar_ser=$_GET['series'];
	
	}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>

</head>

<body>
  
      <form id="form1"  name="form1" method="get" action="show.php">
        <select id="mark" name="mark">
          <option value="">--</option>
          <option value="100"<? if($papar_car=="100")echo "selected='selected'"; ?>>BMW</option>
          <option value="101"<? if($papar_car=="101")echo "selected='selected'"; ?>>Audi</option>
        </select>
        <select id="series" name="series">
          <option value="">--</option>
          
          <option value="1" class="100" <? if($papar_ser=="1")echo "selected='selected'"; ?>>1 series</option>
          <option value="3" class="100"<? if($papar_ser=="3")echo "selected='selected'"; ?>>3 series</option>
          <option value="5" class="100"<? if($papar_ser=="5")echo "selected='selected'"; ?>>5 series</option>
          <option value="6" class="100"<? if($papar_ser=="6")echo "selected='selected'"; ?>>6 series</option>
          <option value="7" class="100<? if($papar_ser=="7")echo "selected='selected'"; ?>">7 series</option>
          
          <option value="11" class="101" <? if($papar_ser=="11")echo "selected='selected'"; ?>>A1</option>
          <option value="23" class="101" <? if($papar_ser=="23")echo "selected='selected'"; ?>>A3</option>
          <option value="33" class="101"<? if($papar_ser=="33")echo "selected='selected'"; ?>>S3</option>
          <option value="44" class="101" <? if($papar_ser=="44")echo "selected='selected'"; ?>>A4</option>
          <option value="54" class="101"<? if($papar_ser=="54")echo "selected='selected'"; ?>>S4</option>
          
        </select>
        
		 <button name="" type="submit" > Find! </button> 
              </p>
	      
      </form>
      
			<script type="text/javascript" language="javascript">		  
		  var car_m= <?php echo $_POST['mark']; ?>
		  </script>
		  
		  <script type="text/javascript" language="javascript">		  
		  var car_m_s= <?php echo $_POST['series']; ?>
		  </script>

  <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js" type="text/javascript" charset="utf-8"></script>
  <script src="js/jquery.chained.js" type="text/javascript" charset="utf-8"></script>  
  <script type="text/javascript" charset="utf-8">
  $(function() {    
    
    $("#series").chained("#mark");   
    
  });
  </script>
guys, after i done selection in the form1, i press submit button and Im going to show.php page. on show.php page i want categories to be already selected. whats my problem?