I installed this mod http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=1175, which gave me the Checkout button, then I edited the file in that mod (includes/templates/MY_TEMPLATE/sideboxes/tpl_shopping_cart.php) by finding this line
$content .= '<div class="cartBoxCheckout"><a href="' . zen_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL') . '">' . zen_image_button(BUTTON_IMAGE_CHECKOUT, BUTTON_CHECKOUT_ALT) . '</a></div>';
copying it and pasting it right below. Then I edited the copy to say this:
$content .= '<div class="cartBoxCheckout"><a href="' . zen_href_link(FILENAME_SHOPPING_CART, '', 'SSL') . '">' . zen_image_button(BUTTON_IMAGE_VIEW_SMALL, BUTTON_VIEW_SMALL_ALT) . '</a></div>';
so the whole thing looks like
$content .= '<div class="cartBoxCheckout"><a href="' . zen_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL') . '">' . zen_image_button(BUTTON_IMAGE_CHECKOUT, BUTTON_CHECKOUT_ALT) . '</a></div>';
$content .= '<div class="cartBoxCheckout"><a href="' . zen_href_link(FILENAME_SHOPPING_CART, '', 'SSL') . '">' . zen_image_button(BUTTON_IMAGE_VIEW_SMALL, BUTTON_VIEW_SMALL_ALT) . '</a></div>';
You'll have to style the buttons. I left the class name the same for both, and did this in the stylesheet to get them side-by-side and spaced right. You'll have to fiddle with it to suit your site:
.cartBoxCheckout {float:left; margin: .1em .2em 0 .2em;}