How to display posts who share same categories?

Is there any way to display only posts who share same categories?
I’m working on a new custom search and here’s an example:

query_posts(array('cat'=>($name, $city)) );

It shows all posts from both categories. What I want is to display all the people named “Brian” who live in “New Jersey” ONLY.

I tried it using tags instead of cats and it works fine, the problem is that I need this to work with categories.

Is there any genious out there who can figure it out? if not, we have another WordPress mystery to be solved.

Thanx!