See the code below:

<script type="text/javascript" charset="utf-8">
jQuery(document).ready(function() {
  var verifyEmail = '<li id="li_customer_email_verify" class="fc_row fc_customer_email_verify">';
  verifyEmail += '<label class="fc_label_left" for="customer_email_verify">Retype Email<span class="fc_ast">*</span></label>';
  verifyEmail += '<input type="text" value="" autocomplete="off" class="fc_text fc_text_long fc_required" id="customer_email_verify" name="customer_email_verify"/>';
  verifyEmail += '<label style="display: none;" class="fc_error" id="customer_email_verify_error" for="customer_email_verify">Please verify your email address.</label>';
  verifyEmail	+=	'</li>';
  jQuery(verifyEmail).insertAfter('#li_customer_email');
  // Now add the onblur error checking events
  jQuery("#customer_email_verify").blur(function() {
    if (this.value == "") {
      FC.checkout.updateErrorDisplay(this.name,true);
    } else if (this.value != "" && this.value != jQuery('#customer_email').val()) {
      jQuery('label[for="customer_email_verify"].fc_error').text("Email address does not match.");
      FC.checkout.updateErrorDisplay(this.name,true);
    } else {
      FC.checkout.updateErrorDisplay(this.name,false);
    }
  });
  jQuery("#customer_email").blur(function() {
    if (this.value != "" && this.value == jQuery('#customer_email_verify').val()) {
      FC.checkout.updateErrorDisplay(jQuery('#customer_email_verify').attr('name'),false);
    } else if (this.value != "" && this.value != jQuery('#customer_email_verify').val()) {
      FC.checkout.updateErrorDisplay(jQuery('#customer_email_verify').attr('name'),true);
    }
  });
});
</script>

• http://forum.foxycart.com/comments.php?DiscussionID=190&page=1#Item_8