Admin Section for Admins only?

Hi all,

I have made a website using wp ecommerce, they can register and login on the front end to see their account/purchases etc but one thing i am worries about though is that anybody can go to wp-admin and log in and then see the backend (obviously they can’t see much but i don’t want them to be able to see anything)

Is there any way to block access to wp-admin for anybody who isn’t an admin?