How do I add a sidebar to the marketpress product list page and single product page?

Hi WPMU support,
I'm in a bind with setting up my digital download store. First I've installed the Marketpress plugin and have everything setup but I can't seem to add a sidebar to both the product listing page and the single product page. I would like to add a shopping cart widget to the sidebar. Currently the product listing page and single product page is full width and it's hard to know when users want to check out and see their cart. I've been to the documentation and have tried it but then my site went weird and my hosting company to had upload a backup for me to retrieve the previous site. Please help! Thanks.