Query post for ‘selected category’ in archive.php

The easiest way to do this is to simply make a category.php template file, that way you’re not jamming everything into one template with multiple query’s and conditionals.

http://codex.wordpress.org/Template_Hierarchy#Category_display

It is unclear what you mean by “featured”, do you want an url like http://example.com/portfoliography/architecture to have a select posts at the top? Or do you want the category page to feature certain categories above others?