Someone who develops this needs to see the checkout page when a registered user and login isn't required. There is a lot of really bad code where there are variables with php tags in them and it creates a hell-o-va mess on the checkout page.
For example themes/wpsc-shopping_cart_page.php:349-351
<?php $email_markup =
<p class='<?php echo wpsc_checkout_form_element_id(); ?>'>