How do I list products in a category in a custom Marketpress theme?

I'm writing a custom mp_category.php template and want to make it output only the products in the category.

I know I can do this with mp_list_products with the category argument, but that outputs in a standard form and won't work with the custom design I'm building.

I'm trying to replicate that functionality with query_posts but the 'category_name' argument isn't working. Here's what I have:

query_posts(array('post_type' => 'product', 'category_name' => 'foo', 'paged' => false, 'posts_per_page'=>12));

I have multiple products in the 'foo' category but this query loads none of them.

Any ideas?

thanks!