Create e-mail matching validation field

gistfile1.php

<?php if(!$this->isCustomerLoggedIn()): ?>
    <?php $billingFields['email'] = $billingFields['email'].'
        <div class="input-box input-email'.((in_array('email', $formErrors)) ? ' input-error' : '').'">
            <label for="billing:email">'.$this->__('Email Address').' <span class="required">*</span></label><br />
            <input type="text" name="billing[email]" id="billing:email" value="'.$dataHelper->clearDash($this->getQuote()->getBillingAddress()->getEmail()).'" title="'.$this->__('Email Address') .'" class="validate-email required-entry input-text" />
        </div>
        <div class="input-box input-email-repeat'.((in_array('email', $formErrors)) ? ' input-error' : '').'">
            <label for="billing:email-repeat">'.$this->__('Retype Email Address').' <span class="required">*</span></label><br />
            <input type="text" name="billing[email-repeat]" id="billing:email-repeat" value="'.$dataHelper->clearDash($this->getQuote()->getBillingAddress()->getEmail()).'" title="'.$this->__('Repeat Email Address') .'" class="validate-cemail required-entry input-text" />
        </div>
        <script>
            Validation.add("validate-cemail", "'.$this->__('Please make sure that you have typed a matching e-mail address').'", function(v) {
                var vemail = $("billing:email").getValue();
                var vcemail = $("billing:email-repeat").getValue();
                return (vemail == vcemail);
            });
        </script>';
    ?>
<?php endif; ?>