E commerce page

Hi, I have installed WP eCommerce. I plan to make 3 product pages onto the high level manu (main menu on the top). After creating the product categories (PC, clothes, and book) and link all relevant products to each category, the problem I found was, how can I put those 3 pages into my top menu in the homepage? when I went to menu option, it does not have the option in which I can put the eccommerce pages to the menu.