password protect posts in a category

hi,

I would like to password protect a part of a site I’m working on. It’s made of a template showing post from a given category.
It’s similar to this page. our products is a category, each product is a post and the menu on the left allows to navigate in the products.
How can I restrict the access of any link starting by href=”http://chateaudemons.com/tmpev/wordpress/our-products?

Any other suggestion welcome

thanks!