wp e-commerce has a few shortcodes for displaying products, you may be able to use one of these:
display products set as “featured”:
[homepage_products]
show a whole category:
[wpsc_category=1]
the products are stored as a custom post type named “wpsc-product”, so you could also just use all of the built in WordPress functions for querying and displaying posts, along with the wp e-commerce function for displaying the add to cart controls:
<?php echo wpsc_add_to_cart_button(1); ?>