A quick example of how to use hook form alter to change the add to cart form.

template.php

<?php
/**
 * Implements hook_form_alter()
 */
function THEMENAME_form_alter(&$form, &$form_state, $form_id) {
  if (strpos($form_id,"cart_add_to_cart")) {
    // load the node that is rendering the cart form
    $node = node_load(array_pop(explode('_',$form_id)));
    // hide the form
    $form['#access'] = false;
  }
}