Checkbox will not stay checked.

Checkbox will not stay checked.

Hello I'm new to jQuery and I find it to be very useful way in upgrading my forms from my website to have more functionality to them.  I am having a problem with my checkboxes though.  I'm trying to use a check box to show a hidden div and it works good, but when I hit the submit button to do error checking the hidden div is hidden and the check box is unchecked.  Here is a sample of the code that I have.
 
<script type="text/javascript" src="Javascript/jquery-1.4.2.js"></script>
<script type="text/javascript">
 $(document).ready(function(){
  
  //Hide div w/id extra
    $("#extra_reg1").css("display","None");
   





  // Add onclick handler to checkbox w/id addmore1
    $("#addmore1").click(function(){
  
  // If checked
  if ($("#addmore1").is(":checked"))
  {
   //show the hidden div
   $("#extra_reg1").show("slow");
  }
  else
  {   
   //otherwise, hide it
   $("#extra_reg1").hide("slow");
  }
   });













 
 <form action="harvest_registration.php" method="post">
 <input type="checkbox" id="addmore1" tabindex="12" name="addmore1"/>
 
<div id="extra_reg1">
          <p class="grey_italic"><strong>Registrant #2</strong></p></td>
 </div>

 
<input type="submit" name="Submit" id="Submit" value="Submit" tabindex="132" />