Category Templates Displaying Post Problem

Hey Folks, I am in the process of developing a theme that relies heavely on the template/category hiarcy. I have developed several categoy templates that display categories as lists of excerpts. My questions is: When I click on a permalink how can I make that post display in an alternative template? In other words, I want all of the post in Category-6 to be displayed in their own template, not index.php Is there a way to do this in the loop? Do I need to alter the Loop in each category template? or what?