Usually you can not assign permissions to Windows Live Users before they sign in to your site at least one time, because you don't have user ID. Shetab Windows Live Authentication for SharePoint have Automatic resource access assignment mechanism that allows you give the user access by his/her email before she sign in to your site. It will give his/her your specified access as soon as he/she sign in.
Automatic resource access assignment mechanism also help you to give serial number or key to your users and they can grant access to specific resource by entering the key or the serial you given to them or by clicking the link that you send to them. More...